U.S. patent number 7,291,567 [Application Number 11/184,964] was granted by the patent office on 2007-11-06 for silica-based film, method of forming the same, composition for forming insulating film for semiconductor device, interconnect structure, and semiconductor device.
This patent grant is currently assigned to JSR Corporation. Invention is credited to Masahiro Akiyama, Seitaro Hattori, Atsushi Shiota, Hajime Tsuchiya.
United States Patent |
7,291,567 |
Tsuchiya , et al. |
November 6, 2007 |
Silica-based film, method of forming the same, composition for
forming insulating film for semiconductor device, interconnect
structure, and semiconductor device
Abstract
A method of forming a silica-based film includes: applying a
composition for forming an insulating film for a semiconductor
device, which is cured by using heat and ultraviolet radiation, to
a substrate to form a coating; heating the coating; and applying
heat and ultraviolet radiation to the coating to effect a curing
treatment. The composition includes: a hydrolysis-condensation
product produced by hydrolysis and condensation of at least one
silane compound selected from the group consisting of compounds
shown by the following general formula (A), and at least one silane
compound selected from the group consisting of compounds shown by
the following general formula (B) and compounds shown by the
following general formula (C); and an organic solvent,
##STR00001##
Inventors: |
Tsuchiya; Hajime (Kumamoto,
JP), Hattori; Seitaro (Tsukuha, JP),
Akiyama; Masahiro (Tsukuba, JP), Shiota; Atsushi
(Sunnyvale, CA) |
Assignee: |
JSR Corporation (Tokyo,
JP)
|
Family
ID: |
35355579 |
Appl.
No.: |
11/184,964 |
Filed: |
July 20, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060024980 A1 |
Feb 2, 2006 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 23, 2004 [JP] |
|
|
2004-216346 |
|
Current U.S.
Class: |
438/761;
257/E21.271; 257/E21.26 |
Current CPC
Class: |
H01L
21/316 (20130101); H01L 21/02348 (20130101); H01L
21/02164 (20130101); H01L 21/02126 (20130101); C09D
183/10 (20130101); H01L 21/3121 (20130101); H01L
21/02282 (20130101); H01L 21/02211 (20130101); G03F
7/0757 (20130101) |
Current International
Class: |
H01L
21/31 (20060101) |
Field of
Search: |
;438/781 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 317 858 |
|
May 1989 |
|
EP |
|
1 122 770 |
|
Aug 2001 |
|
EP |
|
63-248710 |
|
Oct 1988 |
|
JP |
|
63-289939 |
|
Nov 1988 |
|
JP |
|
1-194980 |
|
Aug 1989 |
|
JP |
|
3-30427 |
|
Feb 1991 |
|
JP |
|
8-29932 |
|
Mar 1996 |
|
JP |
|
2000-109695 |
|
Apr 2000 |
|
JP |
|
2000-290590 |
|
Oct 2000 |
|
JP |
|
2000-313612 |
|
Nov 2000 |
|
JP |
|
2000-327933 |
|
Nov 2000 |
|
JP |
|
2001-110802 |
|
Apr 2001 |
|
JP |
|
2001-279163 |
|
Oct 2001 |
|
JP |
|
2002-38091 |
|
Feb 2002 |
|
JP |
|
2002-288268 |
|
Oct 2002 |
|
JP |
|
2004-59737 |
|
Feb 2004 |
|
JP |
|
2004-149714 |
|
May 2004 |
|
JP |
|
WO 03/025994 |
|
Mar 2003 |
|
WO |
|
Other References
James L. Hedrick, et al. "Templating Nanoporosity in Thin-Film
Dielectric Insulators", Advanced Materials, Research News, vol. 10,
No. 13, 1998 pp. 1049-1053. cited by other .
Ed Mickler, et al., "A Charge Damage Study using an Electron Beam
Low k Treatment", Proceedings of the International Interconnect
Technology Conference, 2004, 190-192. cited by other .
H. Miyajima, et al., "The Application of Simultaneous eBeam Cure
Method for 65 nm node Cu/Low-k Technology with Hybrid (PAE/MSX)
Structure", Proceedings of the International Interconnect
Technology Conference, 2004, 222-224. cited by other .
U.S. Appl. No. 11/432,345, filed May 12, 2006, Shiota. cited by
other .
U.S. Appl. No. 11/393,647, filed Mar. 31, 2006, Shiota. cited by
other .
U.S. Appl. No. 11/596,295, filed Nov. 13, 2006, Akiyama et al.
cited by other .
U.S. Appl. No. 11/596,188, filed Nov. 13, 2006, Akiyama et al.
cited by other .
U.S. Appl. No. 11/484,604, filed Jul. 12, 2006, Nakagawa et al.
cited by other .
U.S. Appl. No. 11/485,508, filed Jul. 13, 2006, Nakagawa et al.
cited by other .
U.S. Appl. No. 11/486,085, filed Jul. 14, 2006, Nakagawa et al.
cited by other .
U.S. Appl. No. 11/489,468, filed Jul. 20, 2006, Akiyama et al.
cited by other .
U.S. Appl. No. 11/580,959, filed Oct. 16, 2006, Akiyama et al.
cited by other .
"STARFIRE.RTM. SP-DEPCS", STARFIRE.RTM. SYSTEMS,
www.starfiresystems.com, May 2005, p. 1. cited by other .
"STARFIRE.RTM. SP-DMPCS", STARFIRE.RTM. SYSTEMS,
www.starfiresystems.com, May 2005, p. 1. cited by other.
|
Primary Examiner: Malsawma; Lex
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A method of forming a silica-based film, the method comprising:
applying a composition for forming an insulating film for a
semiconductor device, which is cured by using heat and ultraviolet
radiation, to a substrate to form a coating; heating the coating;
and applying heat and ultraviolet radiation to the coating to
effect a curing treatment; wherein the composition includes: a
hydrolysis-condensation product produced by hydrolysis and
condensation of at least one silane compound selected from the
group consisting of compounds shown by the following general
formula (A), and at least one silane compound selected from the
group consisting of compounds shown by the following general
formula (B) and compounds shown by the following general formula
(C); and an organic solvent, ##STR00008## wherein R.sup.1 to
R.sup.8 individually represent an alkyl group or an aryl group, and
X represents the following general formula (A1) or (A2),
##STR00009## wherein Y.sup.1 to Y.sup.8 individually represent a
hydrogen atom, a fluorine atom, an alkyl group, or an aryl group,
provided that Y.sup.1 and Y.sup.2 or Y.sup.5 and Y.sup.6 may form a
ring in combination, (R.sup.9).sub.a--Si--(OR.sup.10).sub.4-a (B)
wherein R.sup.9 and R.sup.10 represent an alkyl group or an aryl
group, and a represents an integer from 0 to 3,
R.sup.11.sub.b(R.sup.12O).sub.3-bSi--(R.sup.15).sub.d--Si(OR.sup.13).sub.-
3-cR.sup.14.sub.c (C) wherein R.sup.11 to R.sup.14 individually
represent an alkyl group or an aryl group, b and c individually
represent an integer from 0 to 2, R.sup.15 represents an oxygen
atom, a phenylene group, or a group --(CH.sub.2).sub.m--(wherein m
represents an integer from 1 to 6), and d represents 0 or 1.
2. The method according to claim 1, wherein the heat and the
ultraviolet radiation are applied at the same time.
3. The method according to claim 1, wherein the heating is
performed at 100 to 450.degree. C.
4. The method according to claim 1, wherein the ultraviolet
radiation has a wavelength of 250 nm or less.
5. A silica-based film having a dielectric constant of 1.5 to 3.2,
a film density of 0.7 to 1.3 g/cm.sup.3, and a water contact angle
of 60 degrees or more, the silica-based film being obtained by the
method according to any of claims 1 to 4.
6. An interconnect structure, comprising the silica-based film
according to claim 5 as an interlayer dielectric.
7. A semiconductor device, comprising the interconnect structure
according to claim 6.
8. A composition for forming an insulating film for a semiconductor
device, which is used in the method according to any of claims 1 to
4 and is cured by using heat and ultraviolet radiation, the
composition comprising: a hydrolysis-condensation product produced
by hydrolysis and condensation of at least one silane compound
selected from the group consisting of the compounds shown by the
general formula (A), and at least one silane compound selected from
the group consisting of the compounds shown by the general formula
(B) and the compounds shown by the general formula (C); and an
organic solvent.
9. The composition according to claim 8, wherein the content of the
compounds shown by the general formula (A) in the silane compound
is 60 mol % or less.
10. The composition according to claim 8, wherein two or more
silane compounds selected from the group consisting of the
compounds shown by the general formula (B) and the compounds shown
by the general formula (C) are used.
11. The composition according to claim 10, wherein the two or more
silane compounds selected from the group consisting of the
compounds shown by the general formula (B) and the compounds shown
by the general formula (C) are an alkyltrialkoxysilane and a
tetraalkoxysilane.
12. The composition according to claim 8, which does not include an
ultraviolet radiation active reaction promoter.
13. The composition according to claim 12, wherein the reaction
promoter is one of, or a combination of, a reaction initiator, an
acid generator, a base generator, and a sensitizer having an
ultraviolet radiation absorption function.
14. The composition according to claim 8, wherein the content of
Na, K, and Fe is respectively 100 ppb or less.
15. The composition according to claim 8, wherein the ultraviolet
radiation has a wavelength of 250 nm or less.
Description
Japanese Patent Application No. 2004-216346, filed on Jul. 23,
2004, is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
The present invention relates to a silica-based film, a method of
forming the same, a composition for forming an insulating film for
a semiconductor device, an interconnect structure, and a
semiconductor device.
A silica (SiO.sub.2) film formed by a vacuum process such as a CVD
process has been widely used as an interlayer dielectric for a
semiconductor device used in a large-scale integrated circuit (LSI)
or the like. In recent years, in order to form an interlayer
dielectric having a more uniform thickness, a spin-on-glass (SOG)
film, which is a coating-type insulating film containing an
alkoxysilane hydrolysate as the major component, has also been
used. Along with an increase in the degree of integration of the
LSI, a low-dielectric constant interlayer dielectric containing
organic silica sol represented by methyl silsesquioxane (MSQ) has
also been developed (U.S. Pat. Nos. 6,235,101, 6,413,647, and
6,495,264).
The organic silica sol is cured by causing the silanol group in the
sol to undergo a dehydration-condensation reaction by heating at
350 to 500.degree. C., whereby an insulating film exhibiting a
dielectric constant, mechanical strength, and chemical durability
suitable as an interlayer dielectric for a semiconductor device can
be formed. However, since the reaction of the organic silica sol is
a solid-phase reaction, dehydration-condensation does not rapidly
proceed due to diffusion control. Therefore, it is necessary to
heat the organic silica sol for a long time (e.g. 30 minutes at
least; usually one hour or more). In order to perform such a long
heat treatment, a batch-type heat treatment furnace capable of
treating 50 to 150 wafers at a time has been used to treat a
spin-on low-dielectric-constant interlayer dielectric. A
semiconductor device which mainly requires a
low-dielectric-constant interlayer dielectric is a semiconductor
device in the logic device field. However, a logic device
interconnect manufacturing step has been tending toward a
single-wafer process in which a wafer is rapidly processed one by
one. This is because a mainstream logic device such as an ASIC or a
custom IC is manufactured in a high-variety low-volume production
process. Specifically, the single-wafer process has become the
mainstream manufacturing process in order to improve the degrees of
freedom of the manufacturing steps.
As a method for rapidly curing a low-dielectric-constant interlayer
dielectric composition containing organic silica sol as the major
component while improving the strength, a method using electron
beams has been proposed (U.S. Pat. No. 6,204,201 and European
Patent No. 1122770). This method causes not only a silanol
condensation reaction, but also causes decomposition and activation
of an organic group in the organic silica-based film to introduce a
crosslinked structure such as Si--CH.sub.x--Si. A film exhibiting
low hygroscopicity and excellent mechanical strength can be
obtained by applying electron beams usually within five minutes,
whereby the single-wafer processing can be performed. On the other
hand, accumulation of an electric charge due to electron beam
application may damage the transistor structure in the LSI.
Therefore, arguments exist for and against curing a
low-dielectric-constant interlayer dielectric composition using
electron beams (E. Mickler et al. Proceedings of the International
Interconnect Technology Conference, p190, 2004., (Miyajima, et al.
Proceedings of the International Interconnect Technology
Conference, p. 222, 2004).
A method using ultraviolet radiation is considered as a method for
rapidly curing a low-dielectric-constant interlayer dielectric
composition containing organic silica sol as the major component
without using electron beams. Now, technologies other than the LSI
interlayer dielectric technology are considered below. A technology
of gelling silica sol by adding a photoacid generator or a
photobase generator, which generates an acid or a base upon
exposure to ultraviolet radiation, to silica sol and an
alkoxysilane to promote a condensation reaction of a silanol and an
alkoxide has been known as an optical sol-gel technology, and has
been applied to formation of an optical waveguide or the like (e.g.
Japanese Patent Application Laid-Open No. 2000-109695). A silica
film cured by using a photoacid generator or a photobase generator
generally exhibits high hygroscopicity due to a large amount of
residual silanol. As a result, the resulting film has a high
dielectric constant. The hygroscopicity due to the residual silanol
may be reduced by gelling the silica sol by applying ultraviolet
radiation and heating the resulting product at about 250 to
500.degree. C. for a predetermined time or more (usually 30 minutes
or more). However, this process does not achieve an improvement
over the above-described silica film thermal curing method.
Moreover, a composition containing a photoacid generator or a
photobase generator cannot satisfy the quality as an insulating
film for an LSI semiconductor device for which high insulation
reliability is demanded, since the photoacid generator, the
photobase generator, or an acidic or basic substance generated by
the photoacid generator or the photobase generator functions as a
charge carrier to impair the insulating properties or causes an
interconnect metal to deteriorate.
A siloxane compound is highly transparent to ultraviolet radiation,
and has been vigorously studied as a backbone of an F.sub.2
photoresist using ultraviolet radiation having a wavelength of 157
nm (e.g. Japanese Patent Application Laid-Open No. 2002-288268).
This technology uses a siloxane backbone, but is basically based on
the principle of a chemically-amplified photoresist using a KrF or
ArF light source. Specifically, a photoacid generator generates an
acidic substance upon exposure to ultraviolet radiation, and a
chemical bond cleaved by an acid produces a functional group, such
as a carboxylic acid, which is readily dissolved in a basic
developer. Therefore, this technology does not promote a
crosslinking reaction of silica sol by ultraviolet radiation.
The surface of the organic silica-based film cured by applying
heat, electron beams, or the like has high hydrophobicity. In order
to decrease the surface hydrophobicity, ultraviolet radiation may
be applied to the organic silica-based film (e.g. U.S. Pat. No.
6,383,913, Japanese Patent Application Laid-Open No. 63-248710,
Japanese Patent Application Laid-Open No. 63-289939, Kokoku
publication No. 8-29932, Japanese Patent Application Laid-Open No.
2001-110802). These technologies are characterized in that the
surface of the organic silica-based film is oxidized by ozone
produced by applying ultraviolet radiation in air so that the
hydrophobic surface is changed into a hydrophilic surface having
high reactivity, such as a silanol. This modification treatment is
mainly performed in order to improve adhesion to a film deposited
as the upper layer.
As described above, a technology of applying a polysiloxane resin
solution or an organic silica sol solution to a substrate and
applying ultraviolet radiation to the resulting film has been
widely studied. However, a technology which uses ultraviolet
radiation for curing organic silica sol in order to form an
interlayer dielectric for an LSI semiconductor device is limited.
Japanese Patent Application Laid-Open No. 3-30427, Japanese Patent
Application Laid-Open No. 1-194980, International Patent
Application No. WO 03/025994, and U.S. patent application Ser. No.
2004/0058090 disclose such limited related-art technologies.
Japanese Patent Application Laid-Open No. 3-30427 discloses a
technology in which a solution prepared by dissolving a
tetraalkoxysilane (e.g. tetraethoxysilane: TEOS) in collodion is
applied to a semiconductor substrate, and ultraviolet radiation is
applied to the solution in a nitrogen atmosphere to obtain a
silicon dioxide film at a low temperature. The feature of this
technology is that highly volatile TEOS is fixed using the
collodion, and decomposition of the collodion and dehydration and
condensation of TEOS are promoted by applying ultraviolet
radiation. Japanese Patent Application Laid-Open No. 1-194980
discloses a technology in which an organosiloxane resin is applied
to a substrate, ultraviolet radiation having a dominant wavelength
of 254 nm is applied to the resin at a temperature of 200.degree.
C. or less to oxidize the surface of the organosiloxane film by
ozone produced by ultraviolet radiation, and the oxidized film is
heated at 400.degree. C. or more, particularly about 900.degree. C.
to obtain a dense silicon dioxide film.
International Patent Application No. WO 03/025994 and U.S. patent
application No. 2004/58090 disclose a technology of curing
hydrogenated silsesquioxane (HSQ) or MSQ by applying ultraviolet
radiation. In this technology, ultraviolet radiation is applied to
HSQ or HSQ/MSQ cocondensate in the presence of oxygen so that
active oxygen (e.g. ozone) produced in the system promotes
oxidation of Si--H in HSQ to form a silica film containing a large
amount of SiO.sub.2 bond. These references describe that this
technology is also effective for curing MSQ in the presence of
oxygen rather than the absence of oxygen. Therefore, it is
estimated that the SiO.sub.2 bond formed by active oxygen is the
principal mechanism of the crosslinking reaction. The feature of
this technology is the use of ultraviolet radiation, since it is
impossible to form the SiO.sub.2 bond in a short time using other
curing methods. However, while a silica film formed according to
this technology has a high modulus of elasticity and high hardness
due to an increase in the amount of the SiO.sub.2 bond, the
moisture absorption and the dielectric constant are increased due
to an increase in hydrophilicity of the film. A film having high
hygroscopicity generally tends to be damaged by reactive ion
etching (RIE) performed in the processing of an interlayer
dielectric of a semiconductor device, and exhibits insufficient
chemical resistance against a wet cleaning liquid. This tendency
significantly occurs in a low-dielectric-constant interlayer
dielectric having a porous structure with a dielectric constant k
of 2.5 or less. Therefore, (a) an organic silica sol composition
which does not include an ionic substance such as a photoacid
generator, photobase generator, or photosensitizer, a charge
carrier, or a corrosive compound generation source, and can be
cured in a short time, (b) a method for curing an organic
silica-based film which does not cause damage to a transistor
structure and enables single-wafer processing, (c) an organic
silica-based film which does not exhibit hygroscopicity and
exhibits high hydrophobicity, and (d) an organic silica-based film
which exhibits such mechanical strength that the organic
silica-based film can withstand formation of a copper damascene
structure, are demanded as a low-dielectric-constant interlayer
dielectric for an LSI semiconductor device along with a method of
forming the same.
An organic silica sol composition for a low-dielectric-constant
insulating film used for a semiconductor device is generally
designed so that the composition of the organic silica sol is
controlled so that an organic silica film obtained by curing the
composition by heating has a high modulus of elasticity, taking
into consideration the yield in a step in which a dynamic stress
occurs, such as chemical mechanical polishing (CMP) or packaging
(e.g. U.S. Pat. No. 6,495,264). In more detail, the organic silica
sol composition is designed so that the absolute crosslink density
in the silica film is increased by increasing the amount of silicon
atom which bonds to four oxygen atoms (hereinafter called
"component Q") in the organic silica sol to usually 40 mol % or
more. The crosslink density is increased by increasing the amount
of component Q, whereby a film having a high modulus of elasticity
and high hardness can be obtained. However, it is difficult to
cause the crosslink site (silanol) of the component Q to completely
react. If the amount of component Q is increased to a large extent,
the amount of residual silanol is increased after thermal curing,
whereby the resulting film exhibits hydrophilicity and high
hygroscopicity. In order to compensate for this drawback,
cocondensation with an alkoxysilane having a hydrophobic group such
as a methyltrialkoxysilane is carried out using a basic catalyst
(e.g. ammonia or tetraalkylhydroxyammonium) to produce a sol having
a high degree of condensation to reduce the absolute amount of
silanol in the sol (U.S. Pat. No. 6,413,647), or the sol having a
high degree of condensation is subjected to an additional
hydrophobic treatment (Japanese Patent Application Laid-Open No.
2004-59737 and Japanese Patent Application Laid-Open No.
2004-149714). However, since the organic silica sol containing a
large amount of component Q has a low molecular chain mobility due
to high crosslink density, the diffusion barrier during the
solid-phase reaction is very high. The condensation reaction is not
promoted even if the organic silica sol containing a large amount
of component Q is cured at 400.degree. C. while applying
ultraviolet radiation within five minutes. Therefore, a curing time
of 30 minutes or more is required for causing the organic silica
sol to react.
SUMMARY
A first aspect of the invention relates to a method of forming a
silica-based film, the method comprising:
applying a composition for forming an insulating film for a
semiconductor device, which is cured by using heat and ultraviolet
radiation, to a substrate to form a coating;
heating the coating; and
applying heat and ultraviolet radiation to the coating to effect a
curing treatment;
wherein the composition includes:
a hydrolysis-condensation product produced by hydrolysis and
condensation of at least one silane compound selected from the
group consisting of compounds shown by the following general
formula (A), and at least one silane compound selected from the
group consisting of compounds shown by the following general
formula (B) and compounds shown by the following general formula
(C); and
an organic solvent,
##STR00002## wherein R.sup.1 to R.sup.8 individually represent an
alkyl group or an aryl group, and X represents the following
general formula (A1) or (A2),
##STR00003## wherein Y.sup.1 to Y.sup.8 individually represent a
hydrogen atom, a fluorine atom, an alkyl group, or an aryl group,
provided that Y.sup.1 and Y.sup.2 or Y.sup.5 and Y.sup.6 may form a
ring in combination, (R.sup.9).sub.a--Si--(OR.sup.10).sub.4-a (B)
wherein R.sup.9 and R.sup.10 represent an alkyl group or an aryl
group, and a represents an integer from 0 to 3,
R.sup.11.sub.b(R.sup.12O).sub.3-bSi--(R.sup.15).sub.d--Si(OR.sup.13).sub.-
3-cR.sup.14.sub.c (C) wherein R.sup.11 to R.sup.14 individually
represent an alkyl group or an aryl group, b and c individually
represent an integer from 0 to 2, R.sup.15 represents an oxygen
atom, a phenylene group, or a group --(CH.sub.2).sub.m--(wherein m
represents an integer from 1 to 6), and d represents 0 or 1.
A second aspect of the invention relates to a silica-based film
having a dielectric constant of 1.5 to 3.2, a film density of 0.7
to 1.3 g/cm.sup.3, and a water contact angle of 60 degrees or more,
the silica-based film being obtained by the above method.
A third aspect of the invention relates to an interconnect
structure, comprising the above silica-based film as an interlayer
dielectric.
A fourth aspect of the invention relates to a semiconductor device,
comprising the above interconnect structure.
A fifth aspect of the invention relates to a composition for
forming an insulating film for a semiconductor device, which is
used in the above method and is cured by using heat and ultraviolet
radiation, the composition comprising:
a hydrolysis-condensation product produced by hydrolysis and
condensation of at least one silane compound selected from the
group consisting of the compounds shown by the general formula (A),
and at least one silane compound selected from the group consisting
of the compounds shown by the general formula (B) and the compounds
shown by the general formula (C); and
an organic solvent.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1 shows an FT-IR spectrum.
FIG. 2 shows .sup.13C-CPMAS NMR.
DETAILED DESCRIPTION OF THE EMBODIMENT
The invention may provide a method of forming a silica-based film
capable of forming a silica-based film having a low dielectric
constant, excellent mechanical strength, and high hydrophobicity in
a short heating time using an insulating film forming composition
according to one embodiment of the invention, and a silica-based
film.
The invention may also provide a composition for forming an
insulating film for a semiconductor device which may be suitably
used in the manufacture of an LSI semiconductor device for which an
increase in the degree of integration and an increase in the number
of layers have been demanded, enables a reduction in heating time
by application of ultraviolet radiation, and can form an insulating
film having a low dielectric constant and excellent mechanical
strength or the like.
The invention may further provide an interconnect structure
including the organic silica-based film according to one embodiment
of the invention, and a semiconductor device including the
interconnect structure.
A method of forming a silica-based film according to an embodiment
of the invention includes:
applying a composition for forming an insulating film for a
semiconductor device, which is cured by using heat and ultraviolet
radiation, to a substrate to form a coating;
heating the coating; and
applying heat and ultraviolet radiation to the coating to effect a
curing treatment;
wherein the composition includes:
a hydrolysis-condensation product produced by hydrolysis and
condensation of at least one silane compound selected from the
group consisting of compounds shown by the following general
formula (A), and at least one silane compound selected from the
group consisting of compounds shown by the following general
formula (B) and compounds shown by the following general formula
(C); and
an organic solvent,
##STR00004## wherein R.sup.1 to R.sup.8 individually represent an
alkyl group or an aryl group, and X represents the following
general formula (A1) or (A2),
##STR00005## wherein Y.sup.1 to Y.sup.8 individually represent a
hydrogen atom, a fluorine atom, an alkyl group, or an aryl group,
provided that Y.sup.1 and Y.sup.2 or Y.sup.5 and Y.sup.6 may form a
ring in combination, (R.sup.9).sub.a--Si--(OR.sup.10).sub.4-a (B)
wherein R.sup.9 and R.sup.10 represent an alkyl group or an aryl
group, and a represents an integer from 0 to 3,
R.sup.11.sub.b(R.sup.12O).sub.3-bSi--(R.sup.15).sub.d--Si(OR.sup.13).sub.-
3-cR.sup.14.sub.c (C) wherein R.sup.11 to R.sup.14 individually
represent an alkyl group or an aryl group, b and c individually
represent an integer from 0 to 2, R.sup.15 represents an oxygen
atom, a phenylene group, or a group --(CH.sub.2).sub.m-- (wherein m
represents an integer from 1 to 6), and d represents 0 or 1.
With this method, the heat and the ultraviolet radiation may be
applied at the same time.
With this method, the heating may be performed at 100 to
450.degree. C.
With this method, the ultraviolet radiation may have a wavelength
of 250 nm or less.
This silica-based film has a dielectric constant of 1.5 to 3.2, a
film density of 0.7 to 1.3 g/cm.sup.3, and a water contact angle of
60 degrees or more.
An interconnect structure according to an embodiment of the
invention includes the above silica-based film as an interlayer
dielectric. A semiconductor device according to an embodiment of
the invention includes the above interconnect structure.
A composition for forming an insulating film for a semiconductor
device according to an embodiment of the invention is used in the
above method, is cured by using heat and ultraviolet radiation, and
includes:
a hydrolysis-condensation product produced by hydrolysis and
condensation of at least one silane compound selected from the
group consisting of the compounds shown by the general formula (A),
and at least one silane compound selected from the group consisting
of the compounds shown by the general formula (B) and the compounds
shown by the general formula (C); and
an organic solvent.
With this composition, the content of the compounds shown by the
general formula (A) in the silane compound may be 60 mol % or
less.
With this composition, two or more silane compounds selected from
the group consisting of the compounds shown by the general formula
(B) and the compounds shown by the general formula (C) may be
used.
With this composition, the two or more silane compounds selected
from the group consisting of the compounds shown by the general
formula (B) and the compounds shown by the general formula (C) may
be an alkyltrialkoxysilane and a tetraalkoxysilane.
This composition may not include an ultraviolet radiation active
reaction promoter. The reaction promoter may be one of, or a
combination of, a reaction initiator, an acid generator, a base
generator, and a sensitizer having an ultraviolet radiation
absorption function.
With this composition, the content of Na, K, and Fe may be
respectively 100 ppb or less.
With this composition, the ultraviolet radiation may have a
wavelength of 250 nm or less.
An insulating film having a low dielectric constant and excellent
mechanical strength or the like can be formed by applying the
composition for forming an insulating film for a semiconductor
device (hereinafter simply called "film forming composition"), that
is, an organic silica sol composition having a specific composition
range, to a substrate, drying the applied composition, and curing
the dried composition by heating and ultraviolet radiation
application.
The features of a film forming composition and a method of forming
a silica-based film according to one embodiment of the invention
are described below.
Embodiments of the present invention are described below in
detail.
1. Film Forming Composition
A film forming composition according to the invention is cured by
using heat and ultraviolet radiation and includes:
a hydrolysis-condensation product (organic silica sol) having an
organic group including a carbon-carbon double bond shown by the
general formula (A1) or (A2), the hydrolysis-condensation product
being produced by hydrolysis and condensation of at least one
silane compound selected from the group consisting of compounds
shown by the following general formula (A), and at least two silane
compounds selected from the group consisting of compounds shown by
the following general formulas (B) and (C); and
an organic solvent,
##STR00006## wherein R.sup.1 to R.sup.8 individually represent
alkyl groups, and X represents the following general formula (A1)
or (A2),
##STR00007## wherein Y.sup.1 to Y.sup.8 individually represent a
hydrogen atom, a fluorine atom, an alkyl group, or an aryl group,
provided that Y.sup.1 and Y.sup.2 or Y.sup.5 and Y.sup.6 may form a
ring in combination, (R.sup.9).sub.a--Si--(OR.sup.10).sub.4-a (B)
wherein R.sup.9 represents an alkyl group or an aryl group,
R.sup.10 represents an alkyl group or an aryl group, and a
represents an integer from 0 to 3,
R.sup.11.sub.b(R.sup.12O).sub.3-bSi--(R.sup.15).sub.d--Si(OR.sup.13).sub.-
3-cR.sup.14.sub.c (C) wherein R.sup.11 to R.sup.14 individually
represent an alkyl group or an aryl group, b and c individually
represent an integer from 0 to 2, R.sup.15 represents an oxygen
atom, a phenylene group, or a group --(CH.sub.2).sub.m-- (wherein m
represents an integer from 1 to 6), and d represents 0 or 1.
The silane compound, composition, organic solvent, additive, and
the like are described below in detail.
1.1 Silane Compound
As the compound shown by the general formula (A) (hereinafter may
be called "compound 1"), the compound shown by the general formula
(B) (hereinafter may be called "compound 2"), and the compound
shown by the general formula (C) (hereinafter may be called
"compound 3"), the following compounds may be used.
1.1.1 Compound 1
The compound 1 shown by the general formula (A) is a silane
compound including an organic group including a carbon-carbon
double bond shown by the general formula (A1) or (A2).
In the general formula (A), R.sup.1 to R.sup.8 individually
represent an alkyl group or an aryl group. As examples of the alkyl
group, a methyl group, an ethyl group, a propyl group, a butyl
group, and the like can be given. The alkyl group preferably
includes 1 to 5 carbon atoms. The alkyl group may be either linear
or branched. A hydrogen atom in the alkyl group may be replaced by
a fluorine atom or the like. As examples of the aryl group, a
phenyl group, a naphthyl group, a methylphenyl group, an
ethylphenyl group, a chlorophenyl group, a bromophenyl group, a
fluorophenyl group, and the like can be given.
In the general formula (A), X is represented by the general formula
(A1) or (A2). In the general formula (A1) or (A2), Y.sup.1 to
Y.sup.8 individually represent a hydrogen atom, a fluorine atom, an
alkyl group, or an aryl group, provided that Y.sup.1 and Y.sup.2 or
Y.sup.5 and Y.sup.6 may form a ring in combination. As examples of
the alkyl group and the aryl group, the groups illustrated as the
groups R.sup.1 to R.sup.8 in the general formula (A) can be
given.
As examples of the organic group shown by the general formula (A1),
a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl
group, a 2-butenyl group, a 1-pentenyl group, a 1-hexanyl group, a
styryl group, a cyclopentanyl group, a cyclohexenyl group, and the
like can be given.
As examples of the organic group shown by the general formula (A2),
an allyl group, a 2-methylpropenyl group, a 2-butenyl group, a
cinnamyl group, a cyclopentenylmethyl group, a cyclohexenylmethyl
group, and the like can be given.
A vinyl group, an allyl group, a 2-isopropenyl group, a styryl
group, and the like can be given as a preferable organic group
shown by the general formula (A1) or (A2).
As specific examples of the compound 1, vinyltrimethoxysilane,
vinyltriethoxysilane, vinyltri-n-propoxysilane,
vinyltri-iso-propoxysilane, vinyltri-n-butoxysilane,
vinyltri-sec-butoxysilane, vinyltri-t-butoxysilane,
vinyltriphenoxysilane, 1-propenyltrimethoxysilane,
1-propenyltriethoxysilane, 2-propenyltrimethoxysilane,
2-propenyltriethoxysilane, 2-propenyltri-n-propoxysilane,
2-propenyltri-iso-propoxysilane, 2-propenyltri-n-butoxysilane,
2-propenyltri-sec-butoxysilane, 2-propenyltri-t-butoxysilane,
2-propenyltriphenoxysilane, 1-butenyltrimethoxysilane,
1-butenyltriethoxysilane, 1-pentenyltrimethoxysilane,
1-pentenyltriethoxysilane, 1-hexenyltrimethoxysilane,
1-hexenyltriethoxysilane, styryltrimethoxysilane,
styryltriethoxysilane, styryltri-n-propoxysilane,
styryltri-iso-propoxysilane, styryltri-n-butoxysilane,
styryltri-sec-butoxysilane, styryltri-t-butoxysilane,
styryltriphenoxysilane, cyclopentenyltrimethoxysilane,
cyclopentenyltriethoxysilane, cyclohexenyltrimethoxysilane,
clyclohexenyltriethoxysilane, allyltrimethoxysilane,
allyltriethoxysilane, allyltri-n-propoxysilane,
allyltri-iso-propoxysilane, allyltri-n-butoxysilane,
allyltri-sec-butoxysilane, allyltri-t-butoxysilane,
allyltriphenoxysilane, 2-methyl propenyltrimethoxysilane, and
2-methyl propenyltriethoxysilane, 2-butenyltrimethoxysilane,
2-butenyltriethoxysilane, (cyclopentenyl)methyltrimethoxysilane,
(cyclopentenyl)methyltriethoxysilane,
(cyclohexenyl)methyltrimethoxysilane,
(cyclohexenyl)methyltriethoxysilane, divinyldimethoxysilane,
divinyldiethoxysilane, divinyldi-n-propoxysilane,
divinyldi-iso-propoxysilane, divinyldi-n-butoxysilane,
divinyldi-sec-butoxysilane, divinyldi-t-butoxysilane,
divinyldiphenoxysilane, di-1-propenyldimethoxysilane,
di-1-propenyldiethoxysilane, di-2-propenyldimethoxysilane,
di-2-propenyldiethoxysilane, di-2-propenyldi-n-propoxysilane,
di-2-propenyldi-iso-propoxysilane, di-2-propenyldi-n-butoxysilane,
di-2-propenyldi-sec-butoxysilane, di-2-propenyldi-t-butoxysilane,
di-2-propenyldiphenoxysilane, di-1-butenyldimethoxysilane,
di-1-butenyldiethoxysilane, di-1-pentenyldimethoxysilane,
di-1-pentenyldiethoxysilane, di-1-hexanyldimethoxysilane,
di-1-hexanyldiethoxysilane, distyryldimethoxysilane,
distyryldiethoxysilane, distyryldi-n-propoxysilane,
distyryldi-iso-propoxysilane, distyryldi-n-butoxysilane,
distyryldi-sec-butoxysilane, distyryldi-t-butoxysilane,
distyryldiphenoxysilane, dicyclopentenyldimethoxysilane,
dicyclopentenyldiethoxysilane, dicyclohexenyldimethoxysilane,
dicyclohexenyldiethoxysilane, diallyldimethoxysilane,
diallyldiethoxysilane, diallyldi-n-propoxysilane,
diallyldi-iso-propoxysilane, diallyldi-n-butoxysilane,
diallyldi-sec-butoxysilane, diallyldi-t-butoxysilane,
diallyldiphenoxysilane, di-2-methylpropenyldimethoxysilane,
di-2-methyl propenyldiethoxysilane, di-2-butenyldimethoxysilane,
di-2-butenyldiethoxysilane, di(cyclopentenyl)methyldimethoxysilane,
di(cyclopentenyl)methyldiethoxysilane,
di(cyclohexenyl)methyldimethyloxysilane,
di(cyclohexenyl)methyldiethoxysilane, methylvinyldimethoxysilane,
methylvinyldiethoxysilane, methylvinyldi-n-propoxysilane,
methylvinyldi-iso-propoxysilane, methylvinyldi-n-butoxysilane,
methylvinyldi-sec-butoxysilane, methylvinyldi-t-butoxysilane,
methylvinyldiphenoxysilane, ethylvinyldimethoxysilane,
ethylvinyldiethoxysilane, n-propylvinyldimethoxysilane,
n-propylvinyldiethoxysilane, iso-propylvinyldimethoxysilane,
iso-propylvinyldiethoxysilane, n-butylvinyldimethoxysilane,
n-butylvinyldiethoxysilane, iso-butylvinyldimethoxysilane,
iso-butylvinyldiethoxysilane, sec-butylvinyldimethoxysilane,
sec-butylvinyldiethoxysilane, tert-butylvinyldimethoxysilane,
tert-butylvinyldiethoxysilane, phenylvinyldimethoxysilane,
phenylvinyldiethoxysilane, methyl-2-propenyldimethoxysilane,
methyl-2-propenyldiethoxysilane, methyl styryldimethoxysilane,
methylstyryldiethoxysilane, allylmethyldimethoxysilane,
allylmethyldiethoxysilane, allylmethyldi-n-propoxysilane,
allylmethyldi-iso-propoxysilane, allylmethyldi-n-butoxysilane,
allylmethyldi-sec-butoxysilane, allylmethyldi-t-butoxysilane,
allylmethyldiphenoxysilane, allylethyldimethoxysilane,
allylethyldiethoxysilane, allyl-n-propyldimethoxysilane,
allyl-n-propyldiethoxysilane, allyl-iso-propyldimethoxysilane,
allyl-iso-propyldiethoxysilane, allyl-n-butyldimethoxysilane,
allyl-n-butyldiethoxysilane, allyl-iso-butyldimethoxysilane,
allyl-iso-butyldiethoxysilane, allyl-sec-butyldimethoxysilane,
allyl-sec-butyldiethoxysilane, allyl-t-butyldimethoxysilane,
allyl-t-butyldiethoxysilane, allylphenyldimethoxysilane,
allylphenyldiethoxysilane, and the like can be given.
Of these, vinyltrimethoxysilane, vinyltriethoxysilane,
2-propenyltrimethoxysilane, 2-propenyltriethoxysilane,
styryltrimethoxysilane, styryltriethoxysilane,
allyltrimethoxysilane, allyltriethoxysilane, divinyldiethoxysilane,
di-2-propenyldimethoxysilane, di-2-propenyldiethoxysilane,
distyryldimethoxysilane, distyryldiethoxysilane,
diallyldimethoxysilane, diallyldiethoxysilane,
methylvinyldimethoxysilane, methylvinyldiethoxysilane,
allylmethyldimethoxysilane, allylmethyldiethoxysilane, and the like
are particularly preferable as the compound 1.
1.1.2 Compound 2
As examples of R.sup.9 to R.sup.10 in the general formula (B), the
groups illustrated as the groups R.sup.1 to R.sup.8 in the general
formula (A) can be given.
As examples of the compounds shown by the general formula (B) in
which a is 0, tetramethoxysilane, tetraethoxysilane,
tetra-n-propoxysilane, tetra-iso-propoxysilane,
tetra-n-butoxysilane, tetra-sec-butoxysilane, tetra-t-butoxysilane,
tetraphenoxysilane, and the like can be given. Of these,
tetramethoxysilane and tetraethoxysilane are preferable. These
compounds may be used either individually or in combination of two
or more.
As examples of the compounds shown by the general formula (B) in
which a is 1, methyltrimethoxysilane, methyltriethoxysilane,
methyltri-n-propoxysilane, methyltriisopropoxysilane,
methyltri-n-butoxysilane, methyltri-sec-butoxysilane,
methyltri-t-butoxysilane, methyltriphenoxysilane,
ethyltrimethoxysilane, ethyltriethoxysilane,
ethyltri-n-propoxysilane, ethyltriisopropoxysilane,
ethyltri-n-butoxysilane, ethyltri-sec-butoxysilane,
ethyltri-t-butoxysilane, ethyltriphenoxysilane,
n-propyltrimethoxysilane, n-propyltriethoxysilane,
n-propyltri-n-propoxysilane, n-propyltriisopropoxysilane,
n-propyltri-n-butoxysilane, n-propyltri-sec-butoxysilane,
n-propyltri-t-butoxysilane, n-propyltriphenoxysilane,
isopropyltrimethoxysilane, isopropyltriethoxysilane,
isopropyltri-n-propoxysilane, isopropyltriisopropoxysilane,
isopropyltri-n-butoxysilane, isopropyltri-sec-butoxysilane,
isopropyltri-t-butoxysilane, iso propyltriphenoxysilane,
n-butyltrimethoxysilane, n-butyltriethoxysilane,
n-butyltri-n-propoxysilane, n-butyltriisopropoxysilane,
n-butyltri-n-butoxysilane, n-butyltri-sec-butoxysilane,
n-butyltri-t-butoxysilane, n-butyltriphenoxysilane,
sec-butyltrimethoxysilane, sec-butyliso-triethoxysilane,
sec-butyltri-n-propoxysilane, sec-butyltriisopropoxysilane,
sec-butyltri-n-butoxysilane, sec-butyltri-sec-butoxysilane,
sec-butyltri-t-butoxysilane, sec-butyltriphenoxysilane,
tert-butyltrimethoxysilane, tert-butyltriethoxysilane,
tert-butyltri-n-propoxysilane, tert-butyltri isopropoxysilane,
tert-butyltri-n-butoxysilane, tert-butyltri-sec-butoxysilane,
tert-butyltri-t-butoxysilane, tert-butyltriphenoxysilane,
trimethoxysilane, triethoxysilane, tri-n-propoxysilane,
triisopropoxysilane, tri-n-butoxysilane, tri-sec-butoxysilane,
tri-t-butoxysilane, and triphenoxysilane can be given. Of these,
methyltrimethoxysilane, methyltriethoxysilane,
methyltri-n-propoxysilane, methyltri-iso-propoxysilane,
ethyltrimethoxysilane, and ethyltriethoxysilane can be given as
preferable compounds. These compounds may be used either
individually or in combination of two or more.
As examples of the compounds shown by the general formula (B) in
which a is 2, dimethyldimethoxysilane, dimethyldiethoxysilane,
dimethyldi-n-propoxysilane, dimethyldiisopropoxysilane,
dimethyldi-n-butoxysilane, dimethyldi-sec-butoxysilane,
dimethyldi-t-butoxysilane, dimethyldiphenoxysilane,
diethyldimethoxysilane, diethyldiethoxysilane,
diethyldi-n-propoxysilane, diethyldiisopropoxysilane,
diethyldi-n-butoxysilane, diethyldi-sec-butoxysilane,
diethyldi-t-butoxysilane, diethyldiphenoxysilane,
di-n-propyldimethoxysilane, di-n-propyldiethoxysilane,
di-n-propyldi-n-propoxysilane, di-n-propyldiisopropoxysilane,
di-n-propyldi-n-butoxysilane, di-n-propyldi-sec-butoxysilane,
di-n-propyldi-t-butoxysilane, di-n-propyldi-phenoxysilane,
diisopropyldimethoxysilane, diisopropyldiethoxysilane,
diisopropyldi-n-propoxysilane, diisopropyldiisopropoxysilane,
diisopropyldi-n-butoxysilane, diisopropyldi-sec-butoxysilane,
diisopropyldi-t-butoxysilane, diisopropyldiphenoxysilane,
di-n-butyldimethoxysilane, di-n-butyldiethoxysilane,
di-n-butyldi-n-propoxysilane, di-n-butyldiisopropoxysilane,
di-n-butyldi-n-butoxysilane, di-n-butyldi-sec-butoxysilane,
di-n-butyldi-t-butoxysilane, di-n-butyldiphenoxysilane,
di-sec-butyldimethoxysilane, di-sec-butyldiethoxysilane,
di-sec-butyldi-n-propoxysilane, di-sec-butyldiisopropoxysilane,
di-sec-butyldi-n-butoxysilane, di-sec-butyldi-sec-butoxysilane,
di-sec-butyldi-t-butoxysilane, di-sec-butyldi-phenoxysilane,
di-t-butyldimethoxysilane, di-t-butyldiethoxysilane,
di-t-butyldi-n-propoxysilane, di-t-butyldiisopropoxysilane,
di-t-butyldi-n-butoxysilane, di-t-butyldi-sec-butoxysilane,
di-t-butyldi-t-butoxysilane, and di-t-butyldi-phenoxysilane, can be
given. Of these, dimethyldimethoxysilane, dimethyldiethoxysilane,
diethyldimethoxysilane, diethyldiethoxysilane, and the like can be
given preferable compounds. These compounds may be used either
individually or in combination of two or more.
As examples of the compounds shown by the general formula (B) in
which a is 3, trimethylmethoxysilane, trimethylethoxysilane,
trimethyl-n-propoxysilane, trimethylisopropoxysilane,
trimethyl-n-butoxysilane, trimethyl-sec-butoxysilane,
trimethyl-t-butoxysilane, trimethylphenoxysilane,
triethylmethoxysilane, and triethylethoxysilane can be given. Of
these, trimethylmethoxysilane, trimethylethoxysilane, and
triethylmethoxysilane can be given preferable compounds. These
compounds may be used either individually or in combination of two
or more.
1.1.3 Compound 3
As examples of R.sup.11 to R.sup.14 in the general formula (C), the
groups illustrated as the groups R.sup.1 to R.sup.8 in the general
formula (A) can be given.
As examples of the compounds shown by the general formula (C) in
which d is 0, hexamethoxydisilane, hexaethoxydisilane,
hexaphenoxydisilane, 1,1,1,2,2-pentamethoxy-2-methyldisilane,
1,1,1,2,2-pentaethoxy-2-methyldisilane,
1,1,1,2,2-pentaphenoxy-2-methyldisilane,
1,1,1,2,2-pentamethoxy-2-ethyldisilane,
1,1,1,2,2-pentaethoxy-2-ethyldisilane,
1,1,1,2,2-pentaphenoxy-2-ethyldisilane,
1,1,1,2,2-pentamethoxy-2-phenyldisilane,
1,1,1,2,2-pentaethoxy-2-phenyldisilane,
1,1,1,2,2-pentaphenoxy-2-phenyldisilane,
1,1,2,2-tetramethoxy-1,2-dimethyldisilane,
1,1,2,2-tetraethoxy-1,2-dimethyldisilane,
1,1,2,2-tetraphenoxy-1,2-dimethyldisilane,
1,1,2,2-tetramethoxy-1,2-diethyldisilane,
1,1,2,2-tetraethoxy-1,2-diethyldisilane,
1,1,2,2-tetraphenoxy-1,2-diethyldisilane,
1,1,2,2-tetramethoxy-1,2-diphenyldisilane,
1,1,2,2-tetraethoxy-1,2-diphenyldisilane,
1,1,2,2-tetraphenoxy-1,2-diphenyldisilane,
1,1,2-trimethoxy-1,2,2-trimethyldisilane,
1,1,2-triethoxy-1,2,2-trimethyldisilane,
1,1,2-triphenoxy-1,2,2-trimethyldisilane,
1,1,2-trimethoxy-1,2,2-triethyldisilane,
1,1,2-triethoxy-1,2,2-triethyldisilane,
1,1,2-triphenoxy-1,2,2-triethyldisilane,
1,1,2-trimethoxy-1,2,2-triphenyldisilane,
1,1,2-triethoxy-1,2,2-triphenyldisilane,
1,1,2-triphenoxy-1,2,2-triphenyldisilane,
1,2-dimethoxy-1,1,2,2-tetramethyldisilane,
1,2-diethoxy-1,1,2,2-tetramethyldisilane,
1,2-diphenoxy-1,1,2,2-tetramethyldisilane,
1,2-dimethoxy-1,1,2,2-tetraethyldisilane,
1,2-diethoxy-1,1,2,2-tetraethyldisilane,
1,2-diphenoxy-1,1,2,2-tetraethyldisilane,
1,2-dimethoxy-1,1,2,2-tetraphenyldisilane,
1,2-diethoxy-1,1,2,2-tetraphenyldisilane,
1,2-diphenoxy-1,1,2,2-tetraphenyldisilane, and the like can be
given.
Of these, hexamethoxydisilane, hexaethoxydisilane,
1,1,2,2-tetramethoxy-1,2-dimethyldisilane,
1,1,2,2-tetraethoxy-1,2-dimethyldisilane,
1,1,2,2-tetramethoxy-1,2-diphenyldisilane,
1,2-dimethoxy-1,1,2,2-tetramethyldisilane,
1,2-diethoxy-1,1,2,2-tetramethyldisilane,
1,2-dimethoxy-1,1,2,2-tetraphenyldisilane,
1,2-diethoxy-1,1,2,2-tetraphenyldisilane, and the like are
preferable.
As examples of the compounds shown by the general formula (C) in
which R.sup.15 is represented by --(CH.sub.2).sub.m--,
bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane,
bis(tri-n-propoxysilyl)methane, bis(tri-i-propoxysilyl)methane,
bis(tri-n-butoxysilyl)methane, bis(tri-sec-butoxysilyl)methane,
bis(tri-t-butoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane,
1,2-bis(triethoxysilyl)ethane, 1,2-bis(tri-n-propoxysilyl)ethane,
1,2-bis(tri-i-propoxysilyl)ethane,
1,2-bis(tri-n-butoxysilyl)ethane,
1,2-bis(tri-sec-butoxysilyl)ethane,
1,2-bis(tri-t-butoxysilyl)ethane,
1-(dimethoxymethylsilyl)-1-(trimethoxysilyl)methane,
1-(diethoxymethylsilyl)-1-(triethoxysilyl)methane,
1-(di-n-propoxymethylsilyl)-1-(tri-n-propoxysilyl)methane,
1-(di-i-propoxymethylsilyl)-1-(tri-i-propoxysilyl)methane,
1-(di-n-butoxymethylsilyl)-1-(tri-n-butoxysilyl)methane,
1-(di-sec-butoxymethylsilyl)-1-(tri-sec-butoxysilyl)methane,
1-(di-t-butoxymethylsilyl)-1-(tri-t-butoxysilyl)methane,
1-(dimethoxymethylsilyl)-2-(trimethoxysilyl)ethane,
1-(diethoxymethylsilyl)-2-(triethoxysilyl)ethane,
1-(di-n-propoxymethylsilyl)-2-(tri-n-propoxysilyl)ethane,
1-(di-i-propoxymethylsilyl)-2-(tri-i-propoxysilyl)ethane,
1-(di-n-butoxymethylsilyl)-2-(tri-n-butoxysilyl)ethane,
1-(di-sec-butoxymethylsilyl)-2-(tri-sec-butoxysilyl)ethane,
1-(di-t-butoxymethylsilyl)-2-(tri-t-butoxysilyl)ethane,
bis(dimethoxymethylsilyl)methane, bis(diethoxymethylsilyl)methane,
bis(di-n-propoxymethylsilyl)methane,
bis(di-i-propoxymethylsilyl)methane,
bis(di-n-butoxymethylsilyl)methane,
bis(di-sec-butoxymethylsilyl)methane,
bis(di-t-butoxymethylsilyl)methane,
1,2-bis(dimethoxymethylsilyl)ethane,
1,2-bis(diethoxymethylsilyl)ethane,
1,2-bis(di-n-propoxymethylsilyl)ethane,
1,2-bis(di-i-propoxymethylsilyl)ethane,
1,2-bis(di-n-butoxymethylsilyl)ethane,
1,2-bis(di-sec-butoxymethylsilyl)ethane,
1,2-bis(di-t-butoxymethylsilyl)ethane,
1,2-bis(trimethoxysilyl)benzene, 1,2-bis(triethoxysilyl)benzene,
1,2-bis(tri-n-propoxysilyl)benzene,
1,2-bis(tri-i-propoxysilyl)benzene,
1,2-bis(tri-n-butoxysilyl)benzene,
1,2-bis(tri-sec-butoxysilyl)benzene,
1,2-bis(tri-t-butoxysilyl)benzene, 1,3-bis(trimethoxysilyl)benzene,
1,3-bis(triethoxysilyl)benzene, 1,3-bis(tri-n-propoxysilyl)benzene,
1,3-bis(tri-i-propoxysilyl)benzene,
1,3-bis(tri-n-butoxysilyl)benzene,
1,3-bis(tri-sec-butoxysilyl)benzene,
1,3-bis(tri-t-butoxysilyl)benzene, 1,4-bis(trimethoxysilyl)benzene,
1,4-bis(triethoxysilyl)benzene, 1,4-bis(tri-n-propoxysilyl)benzene,
1,4-bis(tri-i-propoxysilyl)benzene,
1,4-bis(tri-n-butoxysilyl)benzene,
1,4-bis(tri-sec-butoxysilyl)benzene,
1,4-bis(tri-t-butoxysilyl)benzene, and the like can be given.
Of these, bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane,
1,2-bis(trimethoxysilyl)ethane, 1,2-bis(triethoxysilyl)ethane,
1-(dimethoxymethylsilyl)-1-(trimethoxysilyl)methane,
1-(diethoxymethylsilyl)-1-(triethoxysilyl)methane,
1-(dimethoxymethylsilyl)-2-(trimethoxysilyl)ethane,
1-(diethoxymethylsilyl)-2-(triethoxysilyl)ethane,
bis(dimethoxymethylsilyl)methane, bis(diethoxymethylsilyl)methane,
1,2-bis(dimethoxymethylsilyl)ethane,
1,2-bis(diethoxymethylsilyl)ethane,
1,2-bis(trimethoxysilyl)benzene, 1,2-bis(triethoxysilyl)benzene,
1,3-bis(trimethoxysilyl)benzene, 1,3-bis(triethoxysilyl)benzene,
1,4-bis(trimethoxysilyl)benzene, 1,4-bis(triethoxysilyl)benzene,
and the like are preferable.
The above arbitrary compounds may be used either individually or in
combination of two or more.
1.1.4 Composition of Silane Compound
In the film forming composition of the invention, the total amount
of the compound 1 used is 60 mol % or less, and preferably 5 mol %
or more but 50 mol % or less. If the amount of the compound 1
exceeds 60 mol %, a side reaction other than elimination, such as
polymerization of the substituents shown by the general formula
(A1) or (A2), may occur.
At least one compound may be selected from the group consisting of
the compound 2 and the compound 3. However, if two or more
compounds are selected from the group consisting of the compound 2
and the compound 3, an insulating film provided with well-balanced
performance can be formed.
When using two or more compounds selected from the group consisting
of the compound 2 and the compound 3, it is preferable to select an
alkyltrialkoxysilane and a tetraalkoxysilane.
The film forming composition of the invention may not include a
reaction promoter having ultraviolet radiation activity. The
reaction promoter used herein refers to one of, or a combination
of, a reaction initiator, a catalyst (acid generator or base
generator), and a sensitizer having a UV absorption function. The
feature of the film forming composition of the invention is that
the film forming composition can be cured by ultraviolet radiation
application in combination with heating without using such a
reaction promoter. This is considered to be because the organic
group X of the compound 1 absorbs ultraviolet radiation to undergo
excitation and elimination so that the condensation reaction
proceeds. This is also estimated from examples described later.
Therefore, the film forming composition may include the compound 1
in such a range that oxidation of the substituent or a reaction
between the substituents is not initiated.
When subjecting the compounds 1 to 3 to hydrolysis and
condensation, water may be added in an amount of 0.1 to 100 mol for
one mol of the group represented by OR in the general formulas (A)
to (C).
The hydrolysis-condensation product of the film forming composition
of the invention preferably has a polystyrene-reduced weight
average molecular weight of 500 to 500,000. If the molecular weight
is to great, particles tend to be formed. Moreover, the size of the
pore in the organic silica-based film is increased to a large
extent. If the molecular weight is too small, a problem may occur
relating to applicability and storage stability. The complete
hydrolysis-condensation product used herein refers to a product in
which the groups represented by OR are entirely hydrolyzed to
become OH groups and are completely condensed.
1.1.5 Method of Producing Film Forming Composition
The film forming composition of the invention may be obtained by
mixing the compounds 1 to 3 and an organic solvent containing water
and optionally heating the mixture. As the organic solvent, an
organic solvent described in 1.2 may be used.
In the invention, the hydrolysis and condensation may be carried
out in the presence of a metal chelate compound, an acidic
compound, or a basic compound. The hydrolysis and condensation may
be carried out using the metal chelate compound or the acidic
compound when an insulating film after application and curing has a
dielectric constant of 2.6 to 3.2, and hydrolysis and condensation
may be carried out using the basic compound when an insulating film
has a dielectric constant of 1.5 to 3.0, although the invention is
not limited thereto. The metal chelate compound, the acidic
compound, and the basic compound are described below.
Metal Chelate Compound
The metal chelate compound which may be used at the time of
hydrolysis and condensation of the compounds 1 to 3 is shown by the
following general formula (1).
R.sup.16.sub..beta.M(OR.sup.17).sub..alpha.-.beta. (1) wherein
R.sup.16 represents a chelating agent, M represents a metal atom,
R.sup.17 represents an alkyl group having 2 to 5 carbon atoms or an
aryl group having 6 to 20 carbon atoms, a represents the valence of
the metal M, and .beta. represents an integer from 1 to
.alpha..
As the metal M, at least one metal selected from the group IIIB
metals (aluminum, gallium, indium, and thallium) and the group IVA
metals (titanium, zirconium, and hafnium) is preferable, with
titanium, aluminum, and zirconium being still more preferable.
As specific examples of the metal chelate compound, titanium
chelate compounds such as triethoxy.mono(acetylacetonate)titanium,
tri-n-propoxy.mono(acetylacetonate)titanium,
tri-i-propoxy.mono(acetylacetonate)titanium,
tri-n-butoxy.mono(acetylacetonate)titanium,
tri-sec-butoxy.mono(acetylacetonate)titanium,
tri-t-butoxy.mono(acetylacetonate)titanium,
diethoxy.bis(acetylacetonate)titanium,
di-n-propoxy.bis(acetylacetonate)titanium,
di-i-propoxy.bis(acetylacetonate)titanium,
di-n-butoxy.bis(acetylacetonate)titanium,
di-sec-butoxy.bis(acetylacetonate)titanium,
di-t-butoxy.bis(acetylacetonate)titanium,
monoethoxy.tris(acetylacetonate)titanium,
mono-n-propoxy.tris(acetylacetonate)titanium,
mono-i-propoxy.tris(acetylacetonate)titanium,
mono-n-butoxy.tris(acetylacetonate)titanium,
mono-sec-butoxy.tris(acetylacetonate)titanium,
mono-t-butoxy.tris(acetylacetonate)titanium,
tetrakis(acetylacetonate)titanium,
triethoxy.mono(ethylacetoacetate)titanium,
tri-n-propoxy.mono(ethylacetoacetate)titanium,
tri-i-propoxy.mono(ethylacetoacetate)titanium,
tri-n-butoxy.mono(ethylacetoacetate)titanium,
tri-sec-butoxy.mono(ethylacetoacetate)titanium,
tri-t-butoxy.mono(ethylacetoacetate)titanium,
diethoxy.bis(ethylacetoacetate)titanium,
di-n-propoxy.bis(ethylacetoacetate)titanium,
di-i-propoxy.bis(ethylacetoacetate)titanium,
di-n-butoxy.bis(ethylacetoacetate)titanium,
di-sec-butoxy.bis(ethylacetoacetate)titanium,
di-t-butoxy.bis(ethylacetoacetate)titanium,
monoethoxy.tris(ethylacetoacetate)titanium,
mono-n-propoxy.tris(ethylacetoacetate)titanium,
mono-i-propoxy.tris(ethylacetoacetate)titanium,
mono-n-butoxy.tris(ethylacetoacetate)titanium,
mono-sec-butoxy.tris(ethylacetoacetate)titanium,
mono-t-butoxy.tris(ethylacetoacetate)titanium,
tetrakis(ethylacetoacetate)titanium,
mono(acetylacetonate)tris(ethylacetoacetate)titanium,
bis(acetylacetonate)bis(ethylacetoacetate)titanium, and
tris(acetylacetonate)mono(ethylacetoacetate)titanium; zirconium
chelate compounds such as triethoxy.mono(acetylacetonate)zirconium,
tri-n-propoxy.mono(acetylacetonate)zirconium,
tri-i-propoxy.mono(acetylacetonate)zirconium,
tri-n-butoxy.mono(acetylacetonate)zirconium,
tri-sec-butoxy.mono(acetylacetonate)zirconium,
tri-t-butoxy.mono(acetylacetonate)zirconium,
diethoxy.bis(acetylacetonate)zirconium,
di-n-propoxy.bis(acetylacetonate)zirconium,
di-i-propoxy.bis(acetylacetonate)zirconium,
di-n-butoxy.bis(acetylacetonate)zirconium,
di-sec-butoxy.bis(acetylacetonate)zirconium,
di-t-butoxy.bis(acetylacetonate)zirconium,
monoethoxy.tris(acetylacetonate)zirconium,
mono-n-propoxy.tris(acetylacetonate)zirconium,
mono-i-propoxy.tris(acetylacetonate)zirconium,
mono-n-butoxy.tris(acetylacetonate)zirconium,
mono-sec-butoxy.tris(acetylacetonate)zirconium,
mono-t-butoxy.tris(acetylacetonate)zirconium,
tetrakis(acetylacetonate)zirconium,
triethoxy.mono(ethylacetoacetate)zirconium,
tri-n-propoxy.mono(ethylacetoacetate)zirconium,
tri-i-propoxy.mono(ethylacetoacetate)zirconium,
tri-n-butoxy.mono(ethylacetoacetate)zirconium,
tri-sec-butoxy.mono(ethylacetoacetate)zirconium,
tri-t-butoxy.mono(ethylacetoacetate)zirconium,
diethoxy.bis(ethylacetoacetate)zirconium,
di-n-propoxy.bis(ethylacetoacetate)zirconium,
di-i-propoxy.bis(ethylacetoacetate)zirconium,
di-n-butoxy.bis(ethylacetoacetate)zirconium,
di-sec-butoxy.bis(ethylacetoacetate)zirconium,
di-t-butoxy.bis(ethylacetoacetate)zirconium,
monoethoxy.tris(ethylacetoacetate)zirconium,
mono-n-propoxy.tris(ethylacetoacetate)zirconium,
mono-i-propoxy.tris(ethylacetoacetate)zirconium,
mono-n-butoxy.tris(ethylacetoacetate)zirconium,
mono-sec-butoxy.tris(ethylacetoacetate)zirconium,
mono-t-butoxy.tris(ethylacetoacetate)zirconium,
tetrakis(ethylacetoacetate)zirconium,
mono(acetylacetonate)tris(ethylacetoacetate)zirconium,
bis(acetylacetonate)bis(ethylacetoacetate)zirconium, and
tris(acetylacetonate)mono(ethylacetoacetate) zirconium; and
aluminum chelate compounds such as
triethoxy.mono(acetylacetonate)aluminum,
tri-n-propoxy.mono(acetylacetonate)aluminum,
tri-i-propoxy.mono(acetylacetonate) aluminum,
tri-n-butoxy.mono(acetylacetonate)aluminum,
tri-sec-butoxy.mono(acetylacetonate)aluminum,
tri-t-butoxy.mono(acetylacetonate)aluminum,
diethoxy.bis(acetylacetonate)aluminum,
di-n-propoxy.bis(acetylacetonate)aluminum,
di-i-propoxy.bis(acetylacetonate)aluminum,
di-n-butoxy.bis(acetylacetonate)aluminum,
di-sec-butoxy.bis(acetylacetonate)aluminum,
di-t-butoxy.bis(acetylacetonate)aluminum,
monoethoxy.tris(acetylacetonate)aluminum,
mono-n-propoxy.tris(acetylacetonate)aluminum,
mono-i-propoxy.tris(acetylacetonate)aluminum,
mono-n-butoxy.tris(acetylacetonate)aluminum,
mono-sec-butoxy.tris(acetylacetonate)aluminum,
mono-t-butoxy.tris(acetylacetonate)aluminum,
tetrakis(acetylacetonate)aluminum,
triethoxy.mono(ethylacetoacetate)aluminum,
tri-n-propoxy.mono(ethylacetoacetate)aluminum,
tri-i-propoxy.mono(ethylacetoacetate)aluminum,
tri-n-butoxy.mono(ethylacetoacetate)aluminum,
tri-sec-butoxy.mono(ethylacetoacetate)aluminum,
tri-t-butoxy.mono(ethylacetoacetate)aluminum,
diethoxy.bis(ethylacetoacetate)aluminum,
di-n-propoxy.bis(ethylacetoacetate)aluminum,
di-i-propoxy.bis(ethylacetoacetate)aluminum,
di-n-butoxy.bis(ethylacetoacetate)aluminum,
di-sec-butoxy.bis(ethylacetoacetate)aluminum,
di-t-butoxy.bis(ethylacetoacetate)aluminum,
monoethoxy.tris(ethylacetoacetate)aluminum,
mono-n-propoxy.tris(ethylacetoacetate)aluminum,
mono-i-propoxy.tris(ethylacetoacetate)aluminum,
mono-n-butoxy.tris(ethylacetoacetate)aluminum,
mono-sec-butoxy.tris(ethylacetoacetate)aluminum,
mono-t-butoxy.tris(ethylacetoacetate)aluminum,
tetrakis(ethylacetoacetate)aluminum,
mono(acetylacetonate)tris(ethylacetoacetate)aluminum,
bis(acetylacetonate)bis(ethylacetoacetate)aluminum, and
tris(acetylacetonate)mono(ethylacetoacetate) aluminum can be
given.
In particular, at least one of
(CH.sub.3(CH.sub.3)HCO).sub.4-tTi(CH.sub.3COCH.sub.2COCH.sub.3).sub.t,
(CH.sub.3(CH.sub.3)HCO).sub.4-tTi(CH.sub.3COCH.sub.2COOC.sub.2H.sub.5).su-
b.t,
(C.sub.4H.sub.9O).sub.4-tTi(CH.sub.3COCH.sub.2COCH.sub.3).sub.t,
(C.sub.4H.sub.9O).sub.4-tTi(CH.sub.3COCH.sub.2COOC.sub.2H.sub.5).sub.t,
(C.sub.2H.sub.5(CH.sub.3)CO).sub.4-tTi(CH.sub.3COCH.sub.2COCH.sub.3).sub.-
t,
(C.sub.2H.sub.5(CH.sub.3)CO).sub.4-tTi(CH.sub.3COCH.sub.2COOC.sub.2H.su-
b.5).sub.t,
(CH.sub.3(CH.sub.3)HCO).sub.4-tZr(CH.sub.3COCH.sub.2COCH.sub.3).sub.t,
(CH.sub.3(CH.sub.3)HCO).sub.4-tZr(CH.sub.3COCH.sub.2COOC.sub.2H.sub.5).su-
b.t,
(C.sub.4H.sub.9O).sub.4-tZr(CH.sub.3COCH.sub.2COCH.sub.3).sub.t,
(C.sub.4H.sub.9O).sub.4-tZr(CH.sub.3COCH.sub.2COOC.sub.2H.sub.5).sub.t,
(C.sub.2H.sub.5(CH.sub.3)CO).sub.4-tZr(CH.sub.3COCH.sub.2COCH.sub.3).sub.-
3,
(C.sub.2H.sub.5(CH.sub.3)CO).sub.4-tZr(CH.sub.3COCH.sub.2COOC.sub.2H.su-
b.5).sub.t,
(CH.sub.3(CH.sub.3)HCO).sub.3-tAl(CH.sub.3COCH.sub.2COCH.sub.3).sub.t,
(CH.sub.3(CH.sub.3)HCO).sub.3-tAl(CH.sub.3COCH.sub.2COOC.sub.2H.sub.5).su-
b.t,
(C.sub.4H.sub.9O).sub.3-tAl(CH.sub.3COCH.sub.2COCH.sub.3).sub.t,
(C.sub.4H.sub.9O).sub.3-tAl(CH.sub.3COCH.sub.2COOC.sub.2H.sub.5).sub.t,
(C.sub.2H.sub.5(CH.sub.3)CO).sub.3-tAl(CH.sub.3COCH.sub.2COCH.sub.3).sub.-
t,
(C.sub.2H.sub.5(CH.sub.3)CO).sub.3-tAl(CH.sub.3COCH.sub.2COOC.sub.2H.su-
b.5).sub.t, and the like is preferable as the metal chelate
compound.
The metal chelate compound is used in an amount of 0.0001 to 10
parts by weight, and preferably 0.001 to 5 parts by weight for 100
parts by weight of the compounds 1 to 3 in total (converted to
complete hydrolysis-condensation product) at the time of hydrolysis
and condensation. If the amount of the metal chelate compound is
less than 0.0001 parts by weight, coating applicability may be
decreased. If the amount of the metal chelate compound exceeds 10
parts by weight, the crack resistance of the coating may be
decreased. The metal chelate compound may be added in advance to
the organic solvent at the time of hydrolysis and condensation
together with the compounds 1 to 3, or may be dissolved or
dispersed in water when adding water.
When subjecting the compounds 1 to 3 to hydrolysis and condensation
in the presence of the metal chelate compound, it is preferable to
add water in an amount of 0.5 to 20 mol, and particularly
preferably 1 to 10 mol for one mol of the compounds 1 to 3 in
total. If the amount of water added is less than 0.5 mol, the crack
resistance of the coating may be decreased. If the amount exceeds
20 mol, polymer precipitation or gelation may occur during the
hydrolysis and condensation reaction. It is preferable that the
water be added intermittently or continuously.
Acidic Compound
As the acidic compound which may be used at the time of hydrolysis
and condensation of the compounds 1 to 3, organic acids or
inorganic acids can be given. As examples of the organic acids,
acetic acid, propionic acid, butanoic acid, pentanoic acid,
hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid,
decanoic acid, oxalic acid, maleic acid, methylmalonic acid, adipic
acid, sebacic acid, gallic acid, butyric acid, mellitic acid,
arachidonic acid, shikimic acid, 2-ethylhexanoic acid, oleic acid,
stearic acid, linolic acid, linoleic acid, salicylic acid, benzoic
acid, p-aminobenzoic acid, p-toluenesulfonic acid, benzenesulfonic
acid, monochloroacetic acid, dichloroacetic acid, trichloroacetic
acid, trifluoroacetic acid, formic acid, malonic acid, sulfonic
acid, phthalic acid, fumaric acid, citric acid, tartaric acid,
maleic anhydride, fumaric acid, itaconic acid, succinic acid,
mesaconic acid, citraconic acid, malic acid, malonic acid,
hydrolysate of glutaric acid, hydrolysate of maleic anhydride,
hydrolysate of phthalic anhydride, and the like can be given. As
examples of the inorganic acids, hydrochloric acid, nitric acid,
sulfuric acid, hydrofluoric acid, phosphoric acid, and the like can
be given. In particular, the organic acids are preferable since
polymer precipitation or gelation rarely occurs during the
hydrolysis and condensation reaction. Among the organic acids, a
compound including a carboxyl group is still more preferable. In
particular, acetic acid, oxalic acid, maleic acid, formic acid,
malonic acid, phthalic acid, fumaric acid, itaconic acid, succinic
acid, mesaconic acid, citraconic acid, malic acid, glutaric acid,
and a hydrolysate of maleic anhydride are preferable. These
compounds may be used either individually or in combination of two
or more.
The acidic compound is used in an amount of 0.0001 to 10 parts by
weight, and preferably 0.001 to 5 parts by weight for 100 parts by
weight of the compounds 1 to 3 in total (converted to complete
hydrolysis-condensation product) at the time of hydrolysis and
condensation. If the amount of the acidic compound used is less
than 0.0001 parts by weight, coating applicability may be
decreased. If the amount of the metal chelate compound exceeds 10
parts by weight, the crack resistance of the coating may be
decreased. The acidic compound may be added in advance to the
organic solvent at the time of hydrolysis and condensation together
with the compounds 1 to 3, or may be dissolved or dispersed in
water when adding water.
When subjecting the compounds 1 to 3 to hydrolysis and condensation
in the presence of the acidic compound, it is preferable to add
water in an amount of 0.5 to 20 mol, and particularly preferably 1
to 10 mol for one mol of the compounds 1 to 3 in total. If the
amount of water added is less than 0.5 mol, the crack resistance of
the coating may be decreased. If the amount exceeds 20 mol, polymer
precipitation or gelation may occur during the hydrolysis and
condensation reaction. It is preferable that the water be added
intermittently or continuously.
Basic Compound
As examples of the basic compounds which may be used at the time of
hydrolysis and condensation of the compounds 1 to 3, sodium
hydroxide, potassium hydroxide, lithium hydroxide, cerium
hydroxide, barium hydroxide, calcium hydroxide, pyridine, pyrrole,
piperazine, pyrrolidine, piperidine, picoline, ammonia,
methylamine, ethylamine, propylamine, butylamine, dimethylamine,
diethylamine, dipropylamine, dibutylamine, trimethylamine,
triethylamine, tripropylamine, tributylamine, monoethanolamine,
diethanolamine, dimethylmonoethanolamine, monomethyldiethanolamine,
triethanolamine, diazabicyclooctane, diazabicyclononane,
diazabicycloundecene, urea, tetramethylammonium hydroxide,
tetraethylammonium hydroxide, tetrapropylammonium hydroxide,
tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide,
choline, and the like can be given. Of these, ammonia, organic
amines, and ammonium hydroxides are preferable, with
tetramethylammonium hydroxide, tetraethylammonium hydroxide, and
tetrapropylammonium hydroxide being particularly preferable. The
basic compound may be used either individually or in combination of
two or more.
The basic compound is used in an amount of usually 0.00001 to 1
mol, and preferably 0.00005 to 0.5 mol for one mol of the total
amount of the alkoxyl groups of the compounds 1 to 3. If the amount
of the basic compound used is within the above range, polymer
precipitation or gelation rarely occurs during the reaction.
When subjecting the compounds 1 to 3 to hydrolysis and condensation
in the presence of the basic compound, it is preferable to add
water in an amount of 0.5 to 150 mol, and particularly preferably
0.5 to 130 mol for one mol of the compounds 1 to 3 in total. If the
amount of water added is less than 0.5 mol, the crack resistance of
the coating may be decreased. If the amount exceeds 150 mol,
polymer precipitation or gelation may occur during the hydrolysis
and condensation reaction.
In this case, it is preferable to use an alcohol having a boiling
point of 100.degree. C. or less together with water. As examples of
the alcohol having a boiling point of 100.degree. C. or less used,
methanol, ethanol, n-propanol, and isopropanol can be given. The
alcohol having a boiling point of 100.degree. C. or less is used in
an amount of usually 3 to 100 mol, and preferably 5 to 80 mol for
one mol of the compounds 1 to 3 in total.
The alcohol having a boiling point of 100.degree. C. or less may be
produced during hydrolysis and/or condensation of the compounds 1
to 3. In this case, it is preferable to remove the alcohol having a
boiling point of 100.degree. C. or less by distillation or the like
so that the content becomes 20 wt % or less, and preferably 5 wt %
or less. A dehydrating agent such as methyl orthoformate, a metal
complex, or a leveling agent may be included as an additive.
After obtaining a hydrolysis-condensation product from the
compounds 1 to 3 in the presence of the basic compound, it is
preferable to adjust the pH of the film forming composition (I) of
the invention to 7 or less. As the pH adjustment method, 1) a
method of adding a pH adjustment agent, 2) a method of evaporating
the basic compound from the composition under normal pressure or
reduced pressure, 3) a method of removing the basic compound from
the composition by bubbling a gas such as nitrogen or argon through
the composition, 4) a method of removing the basic compound from
the composition using an ion-exchange resin, 5) a method of
removing the basic compound from the system by extraction or
washing, and the like can be given. These methods may be used in
combination.
As the pH adjustment agent, inorganic acids and organic acids can
be given. As examples of the inorganic acids, hydrochloric acid,
nitric acid, sulfuric acid, hydrofluoric acid, phosphoric acid,
boric acid, oxalic acid, and the like can be given. As examples of
the organic acids, acetic acid, propionic acid, butanoic acid,
pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid,
nonanoic acid, decanoic acid, oxalic acid, maleic acid,
methylmalonic acid, adipic acid, sebacic acid, gallic acid, butyric
acid, mellitic acid, arachidonic acid, shikimic acid,
2-ethylhexanoic acid, oleic acid, stearic acid, linolic acid,
linoleic acid, salicylic acid, benzoic acid, p-aminobenzoic acid,
p-toluenesulfonic acid, benzenesulfonic acid, monochloroacetic
acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic
acid, formic acid, malonic acid, sulfonic acid, phthalic acid,
fumaric acid, citric acid, tartaric acid, succinic acid, itaconic
acid, mesaconic acid, citraconic acid, malic acid, hydrolysate of
glutaric acid, hydrolysate of maleic anhydride, hydrolysate of
phthalic anhydride, and the like can be given. These compounds may
be used either individually or in combination of two or more.
The pH of the composition is adjusted to 7 or less, and preferably
1 to 6 using the pH adjustment agent. The storage stability of the
composition (I) is improved by adjusting the pH within the above
range using the pH adjustment agent. The pH adjustment agent is
used in such an amount that the pH of the composition (I) is within
the above range. The amount of the pH adjustment agent is
appropriately selected.
Organic Solvent
In the invention, the silane compounds 1 to 3 may be subjected to
hydrolysis and condensation in an organic solvent. The organic
solvent is preferably a solvent shown by the following general
formula (2).
R.sup.18O.sup.8(CHCH.sub.3CH.sub.2O).sub..gamma.R.sup.19 (2)
wherein R.sup.18 and R.sup.19 individually represent a hydrogen
atom or a monovalent organic group selected from an alkyl group
having 1 to 4 carbon atoms and CH.sub.3CO--, and .gamma. represents
1 or 2.
As examples of the alkyl groups having 1 to 4 carbon atoms in the
general formula (2), the groups given as the alkyl groups for the
general formula (1) can be given.
As specific examples of the organic solvent shown by the general
formula (2), propylene glycol monomethyl ether, propylene glycol
monoethyl ether, propylene glycol monopropyl ether, propylene
glycol monobutyl ether, propylene glycol dimethyl ether, propylene
glycol diethyl ether, propylene glycol dipropyl ether, propylene
glycol dibutyl ether, dipropylene glycol monomethyl ether,
dipropylene glycol monoethyl ether, dipropylene glycol monopropyl
ether, dipropylene glycol monobutyl ether, dipropylene glycol
dimethyl ether, dipropylene glycol diethyl ether, dipropylene
glycol dipropyl ether, dipropylene glycol dibutyl ether, propylene
glycol monomethyl ether acetate, propylene glycol monoethyl ether
acetate, propylene glycol monopropyl ether acetate, propylene
glycol monobutyl ether acetate, dipropylene glycol monomethyl ether
acetate, dipropylene glycol monoethyl ether acetate, dipropylene
glycol monopropyl ether acetate, dipropylene glycol monobutyl ether
acetate, propylene glycol diacetate, dipropylene glycol diacetate,
and the like can be given. Of these, propylene glycol monomethyl
ether, propylene glycol monoethyl ether, propylene glycol
monopropyl ether, propylene glycol monobutyl ether, propylene
glycol dimethyl ether, propylene glycol diethyl ether, propylene
glycol monomethyl ether acetate, propylene glycol monoethyl ether
acetate, and propylene glycol monopropyl ether acetate are
preferable. These solvents may be used either individually or in
combination of two or more. Another solvent such as an ester
solvent and an amide solvent may be included in a small amount
together with the solvent shown by the general formula (2).
The total solid content of the film forming composition of the
invention is appropriately adjusted depending on the target
application, preferably in the range of 0.1 to 10 wt %. If the
total solid content of the film forming composition of the
invention is 0.1 to 10 wt %, the resulting coating has a thickness
within an appropriate range, and the composition exhibits a more
excellent storage stability. The total solid content is adjusted by
concentration or dilution with an organic solvent, if
necessary.
1.2 Organic Solvent
As the organic solvent which may be used in the invention, at least
one solvent selected from the group consisting of alcohol solvents,
ketone solvents, amide solvents, ether solvents, ester solvents,
aliphatic hydrocarbon solvents, aromatic solvents, and
halogen-containing solvents may be used.
Examples of the alcohol solvents include: monohydric alcohol
solvents such as methanol, ethanol, n-propanol, i-propanol,
n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol,
i-pentanol, 2-methylbutanol, sec-pentanol, t-pentanol,
3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol,
2-ethylbutanol, sec-heptanol, heptanol-3, n-octanol,
2-ethylhexanol, sec-octanol, n-nonyl alcohol,
2,6-dimethylheptanol-4, n-decanol, sec-undecyl alcohol,
trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl
alcohol, furfuryl alcohol, phenol, cyclohexanol,
methylcyclohexanol, 3,3,5-trimethylcyclohexanol, benzyl alcohol,
and diacetone alcohol; polyhydric alcohol solvents such as ethylene
glycol, 1,2-propylene glycol, 1,3-butylene glycol, pentanediol-2,4,
2-methylpentanediol-2,4, hexanediol-2,5, heptanediol-2,4,
2-ethylhexanediol-1,3, diethylene glycol, dipropylene glycol,
triethylene glycol, and tripropylene glycol; polyhydric alcohol
partial ether solvents such as ethylene glycol monomethyl ether,
ethylene glycol monoethyl ether, ethylene glycol monopropyl ether,
ethylene glycol monobutyl ether, ethylene glycol monohexyl ether,
ethylene glycol monophenyl ether, ethylene glycol mono-2-ethylbutyl
ether, diethylene glycol monomethyl ether, diethylene glycol
monoethyl ether, diethylene glycol monopropyl ether, diethylene
glycol monobutyl ether, diethylene glycol monohexyl ether,
propylene glycol monomethyl ether, propylene glycol monoethyl
ether, propylene glycol monopropyl ether, propylene glycol
monobutyl ether, dipropylene glycol monomethyl ether, dipropylene
glycol monoethyl ether, and dipropylene glycol monopropyl ether;
and the like. These alcohol solvents may be used either
individually or in combination of two or more.
As examples of the ketone solvents, acetone, methyl ethyl ketone,
methyl n-propyl ketone, methyl n-butyl ketone, diethyl ketone,
methyl i-butyl ketone, methyl n-pentyl ketone, ethyl n-butyl
ketone, methyl n-hexyl ketone, di-i-butyl ketone, trimethylenonane,
cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone,
2-hexanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone,
diacetone alcohol, acetophenone, fenchone, and the like can be
given. These ketone solvents may be used either individually or in
combination of two or more.
As examples of the amide solvents, nitrogen-containing solvents
such as N,N-dimethylimidazolidinone, N-methylformamide,
N,N-dimethylformamide, N,N-dimethylformamide, acetamide,
N-methylacetamide, N,N-dimethylacetamide, N-methylpropioneamide,
N-methylpyrrolidone, and the like can be given. These amide
solvents may be used either individually or in combination of two
or more.
As examples of the ether solvents, ethyl ether, i-propyl ether,
n-butyl ether, n-hexyl ether, 2-ethylhexyl ether, ethylene oxide,
1,2-propylene oxide, dioxolane, 4-methyl dioxolane, dioxane,
dimethyl dioxane, ethylene glycol monomethyl ether, ethylene glycol
dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol
diethyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol
mono-n-hexyl ether, ethylene glycol monophenyl ether, ethylene
glycol mono-2-ethyl butyl ether, ethylene glycol dibutyl ether,
diethylene glycol monomethyl ether, diethylene glycol dimethyl
ether, diethylene glycol monoethyl ether, diethylene glycol diethyl
ether, diethylene glycol mono-n-butyl ether, diethylene glycol
di-n-butyl ether, diethylene glycol mono-n-hexyl ether, ethoxy
triglycol, tetraethylene glycol di-n-butyl ether, propylene glycol
monomethyl ether, propylene glycol monoethyl ether, propylene
glycol monopropyl ether, propylene glycol monobutyl ether,
dipropylene glycol monomethyl ether, dipropylene glycol monoethyl
ether, tripropylene glycol monomethyl ether, tetrahydrofuran,
2-methyltetrahydrofuran, diphenyl ether, anisole, and the like can
be given. These ether solvents may be used either individually or
in combination of two or more.
As examples of the ester solvents, diethyl carbonate, propylene
carbonate, methyl acetate, ethyl acetate, .gamma.-butyrolactone,
.gamma.-valerolactone, n-propyl acetate, i-propyl acetate, n-butyl
acetate, i-butyl acetate, sec-butyl acetate, n-pentyl acetate,
sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate,
2-ethylbutyl acetate, 2-ethylhexyl acetate, benzyl acetate,
cyclohexyl acetate, methylcyclohexyl acetate, n-nonyl acetate,
methyl acetoacetate, ethyl acetoacetate, ethylene glycol monomethyl
ether acetate, ethylene glycol monoethyl ether acetate, diethylene
glycol monomethyl ether acetate, diethylene glycol monoethyl ether
acetate, diethylene glycol mono-n-butyl ether acetate, propylene
glycol monomethyl ether acetate, propylene glycol monoethyl ether
acetate, propylene glycol monopropyl ether acetate, propylene
glycol monobutyl ether acetate, dipropylene glycol monomethyl ether
acetate, dipropylene glycol monoethyl ether acetate, glycol
diacetate, methoxy triglycol acetate, ethyl propionate, n-butyl
propionate, i-amyl propionate, diethyl oxalate, di-n-butyl oxalate,
methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate,
diethyl malonate, dimethyl phthalate, diethyl phthalate, and the
like can be given. These ester solvents may be used either
individually or in combination of two or more.
As examples of the aliphatic hydrocarbon solvents, n-pentane,
i-pentane, n-hexane, i-hexane, n-heptane, i-heptane,
2,2,4-trimethylpentane, n-octane, i-octane, cyclohexane,
methylcyclohexane, and the like can be given. These aliphatic
hydrocarbon solvents may be used either individually or in
combination of two or more.
As examples of the aromatic hydrocarbon solvents, benzene, toluene,
xylene, ethylbenzene, trimethylbenzene, methylethylbenzene,
n-propylebenzene, i-propylebenzene, diethylbenzene, i-butylbenzene,
triethylbenzene, di-i-propylbenzene, n-amylnaphthalene,
trimethylbenzene, and the like can be given. These aromatic
hydrocarbon solvents may be used either individually or in
combination of two or more. As examples of the halogen-containing
solvents, dichloromethane, chloroform, fluorocarbon, chlorobenzene,
dichlorobenzene, and the like can be given.
In the invention, it is preferable to use an organic solvent having
a boiling point of less than 150.degree. C. As the type of solvent,
an alcohol solvent, a ketone solvent, and an ester solvent are
particularly preferable. It is preferable to use one or more of
these solvents.
1.3 Other Additives
The film forming composition of the invention may further include
components such as an organic polymer, a surfactant, and a silane
coupling agent. These additives may be added to the solvent in
which each component has been dissolved or dispersed before
producing the film forming composition.
1.3.1 Organic Polymer
The organic polymer used in the invention may be added as a readily
decomposable component for forming voids in the silica-based film.
The addition of such an organic polymer is described in references
such as Japanese Patent Application Laid-Open No. 2000-290590,
Japanese Patent Application Laid-Open No. 2000-313612, and Hedrick,
J. L., et al. "Templating Nanoporosity in Thin Film Dielectric
Insulators", Adv. Mater., 10 (13), 1049, 1998. An organic polymer
similar to those described in these references may be added.
As examples of the organic polymer, a polymer having a sugar chain
structure, vinyl amide polymer, (meth)acrylic polymer, aromatic
vinyl compound polymer, dendolimer, polyimide, polyamic acid,
polyarylene, polyamide, polyquinoxaline, polyoxadizole,
fluorine-containing polymer, polymer having a polyalkylene oxide
structure, and the like can be given.
1.3.2 Surfactant
As examples of the surfactant, a nonionic surfactant, an anionic
surfactant, a cationic surfactant, an amphoteric surfactant, and
the like can be given. As specific examples, a fluorine-containing
surfactant, a silicone surfactant, a polyalkylene oxide surfactant,
a poly(meth)acrylate surfactant, and the like can be given. Of
these, the fluorine-containing surfactant and the silicone
surfactant are preferable.
As examples of the fluorine-containing surfactant, compounds having
a fluoroalkyl or fluoroalkylene group in at least one of the
terminal, main chain, and side chain, such as
1,1,2,2-tetrafluorooctyl(1,1,2,2-tetrafluoropropyl)ether,
1,1,2,2-tetrafluorooctylhexyl ether, octaethylene glycol
di(1,1,2,2-tetrafluorobutyl)ether, hexaethylene glycol
(1,1,2,2,3,3-hexafluoropentyl)ether, octapropylene glycol
di(1,1,2,2-tetrafluorobutyl)ether, hexapropylene glycol
di(1,1,2,2,3,3-hexafluoropentyl)ether, sodium
perfluorododecylsulfonate,
1,1,2,2,8,8,9,9,10,10-decafluorododecane,
1,1,2,2,3,3-hexafluorodecane,
N-3-(perfluorooctanesulfonamide)-propyl-N,N'-dimethyl-N-carboxymethylene
ammonium betaine, perfluoroalkyl sulfonamide propyltrimethyl
ammonium salt, perfluoroalkyl-N-ethylsulfonyl glycine salt,
bis(N-perfluorooctylsulfonyl-N-ethylaminoethyl)phosphate, and
monoperfluoroalkylethyl phosphate can be given.
As examples of commercially available products of the
fluorine-containing surfactant, Megafac F142D, F172, F173, F183
(manufactured by Dainippon Ink and Chemicals, Inc.), Eftop EF301,
EF303, EF352 (manufactured by Shin-Akita Kasei Co., Ltd.). Fluorad
FC-430, FC-431 (manufactured by Sumitomo 3M, Ltd.), Asahi Guard
AG710, Surflon S-382, SC-101, SC-102, SC-103, SC-104, SC-105,
SC-106 (manufactured by Asahi Glass Co., Ltd.), BM-1000, BM-1100
(manufactured by BM Chemie), and NBX-15 (manufactured by NEOS Co.,
Ltd.) can be given. Of these, Megafac F172, BM-1000, BM-1100, and
NBX-15 are particularly preferable.
As the silicone surfactant, SH7PA, SH21PA, SH28PA, SH30PA, ST94PA
(manufactured by Toray-Dow Corning Silicone Co., Ltd.) and the like
may be used. Of these, SH28PA and SH30PA are particularly
preferable.
The surfactant is used in an amount of usually 0.00001 to 1 part by
weight for 100 parts by weight of the polymer formed of the
compounds 1 to 3. The surfactant may be used either individually or
in combination of two or more.
1.3.3 Silane Coupling Agent
As examples of the silane coupling agent,
3-glycidyloxypropyltrimethoxysilane,
3-aminoglycidyloxypropyltriethoxysilane,
3-methacryloxypropyltrimethoxysilane,
3-glycidyloxypropylmethyldimethoxysilane,
1-methacryloxypropylmethyldimethoxysilane,
3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,
2-aminopropyltrimethoxysilane, 2-aminopropyltriethoxysilane,
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,
N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,
3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane,
N-ethoxycarbonyl-3-aminopropyltrimethoxysilane,
N-ethoxycarbonyl-3-aminopropyltriethoxysilane,
N-triethoxysilylpropyltriethylenetriamine,
N-triethoxysilylpropyltriethylenetriamine,
10-trimethoxysilyl-1,4,7-triazadecane,
10-triethoxysilyl-1,4,7-triazadecane,
9-trimethoxysilyl-3,6-diazanonylacetate,
9-triethoxysilyl-3,6-diazanonylacetate,
N-benzyl-3-aminopropyltrimethoxysilane,
N-benzyl-3-aminopropyltriethoxysilane,
N-phenyl-3-aminopropyltrimethoxysilane,
N-phenyl-3-aminopropyltriethoxysilane,
N-bis(oxyethylene)-3-aminopropyltrimethoxysilane,
N-bis(oxyethylene)-3-aminopropyltriethoxysilane, and the like can
be given. The silane coupling agent may be used either individually
or in combination of two or more.
2. Film Formation Method
A method of forming a silica-based film according to the invention
includes applying the film forming composition to a substrate to
form a coating, heating the coating, and applying ultraviolet
radiation to the coating to effect a curing treatment.
The curing by ultraviolet radiation application may be performed
under the following conditions. The ultraviolet irradiation has a
wavelength of usually 250 nm or less, but 150 nm or more, and
preferably 150 to 200 nm. It is preferable to use a light source
which emits ultraviolet irradiation having a plurality of
wavelengths in order to prevent a local change in film quality due
to the standing wave caused by reflection from the substrate. The
condensation reaction of the silane compound can be performed at a
low temperature in a short time without using a UV-active reaction
promoter by using ultraviolet radiation having a wavelength within
this range. If ultraviolet radiation having a wavelength exceeding
250 nm is used, a promoting effect on the condensation reaction of
the organic silica sol is not obtained. If the wavelength is too
short, decomposition of the organic group of the organic silica or
elimination of the organic group from the silicon atom may
occur.
In the coating curing treatment of the invention, it is preferable
to perform ultraviolet radiation application and heating at the
same time. The heating may be performed at preferably 100 to
450.degree. C., and still more preferably 250 to 400.degree. C. As
the heating method, a hot plate, ultraviolet radiation lamp
annealing, or the like may be used.
If the coating heating temperature (e.g. substrate temperature) is
lower than 100.degree. C., a sufficient crosslink density may not
be obtained and the coating may not be cured. If the substrate
temperature exceeds 450.degree. C., the resulting film may be
decomposed, thereby making it difficult to conform to the
conditions for the copper damascene interconnect manufacture which
is the main application of the invention.
The ultraviolet radiation may be applied after activating the
coating by heating the substrate at 100 to 450.degree. C. before
applying the ultraviolet radiation to the coating.
In the invention, the ultraviolet radiation application may be
performed in a gas having an oxygen partial pressure of preferably
0.1 kPa or less, and still more preferably 0.01 kPa or less. As the
gas used, N.sub.2, He, Ar, Kr, Xe, CH.sub.4, CO.sub.2, CO, and
H.sub.2O (preferably N.sub.2, He, and Ar) can be given. If the
ultraviolet radiation application is performed in an atmosphere at
a high oxygen concentration, ozone is produced by the ultraviolet
radiation and oxidizes the surface of the film, whereby sufficient
hydrophobicity cannot be maintained.
The ultraviolet radiation application may be performed under normal
pressure, increased pressure, or reduced pressure. The pressure is
preferably 0.001 to 1000 kPa, and still more preferably 0.001 to
101.3 kPa. If the pressure is within the above preferable range,
the elimination reaction is further promoted, whereby the
condensation reaction can be promoted.
In order to control the curing rate of the coating film, step-wise
heating may be performed, or an atmosphere such as nitrogen, air,
oxygen concentration, and pressure may be selected, if necessary. A
silica-based film can be produced by these steps.
As examples of the substrate to which the film forming composition
is applied, Si-containing layers such as Si, SiO.sub.2, SiN, SiC,
and SiCN can be given. As the method for applying the film forming
composition to the substrate, a coating method such as spin
coating, dip coating, roll coating, or spray coating may be used.
After applying the silica-based film forming composition to the
substrate, the solvent is removed to form the coating. A coating
with a dry thickness of 0.05 to 2.5 .mu.m is obtained by single
application, and a coating with a dry thickness of 0.1 to 5.0 .mu.m
is obtained by double application. A silica-based film can be
formed by subjecting the resulting coating to the curing
treatment.
3. Silica-based Film
The silica-based film of the invention has an extremely high
.DELTA.k and modulus of elasticity and exhibits a low dielectric
constant as is clear from examples described later.
The organic silica-based film of the invention has a sufficiently
high crosslink density and high hydrophobicity from the viewpoint
of the .DELTA.k, modulus of elasticity, and the like of the film.
In more detail, the organic silica-based film of the invention has
a dielectric constant of preferably 1.5 to 3.2, and still more
preferably 1.8 to 3.0, a modulus of elasticity of preferably 4.0 to
15.0 GPa, and still more preferably 4.0 to 12.0 GPa, and a film
density of preferably 0.7 to 1.3 g/cm.sup.3, and still more
preferably 0.8 to 1.27 g/cm.sup.3. Therefore, the organic
silica-based film of the invention exhibits excellent insulating
film properties such as mechanical strength and dielectric
constant.
The organic silica-based film of the invention has a water contact
angle of preferably 60 degrees or more, and still more preferably
70 degrees or more. This indicates that the organic silica-based
film of the invention is hydrophobic so that the organic
silica-based film can maintain a low dielectric constant due to low
hygroscopicity. The organic silica-based film is rarely damaged by
RIE used in the semiconductor process due to low hygroscopicity,
and exhibits excellent chemical resistance against a wet cleaning
liquid. In particular, this tendency is significant in an organic
silica-based film having a dielectric constant k of 2.5 or less in
which the insulating film has a porous structure.
As described above, the organic silica-based film of the invention
has characteristics such as (a) excellent insulating film
properties such as a dielectric constant and a modulus of
elasticity and capability of being formed at a low temperature in a
short time since the film forming composition includes an organic
silica sol including a specific substituent, (b) the absence of a
substance contaminating a semiconductor device since it is
unnecessary for the film forming composition to include an ionic
substance such as a UV-active acid generator, base generator, and
photosensitizer, a charge carrier, or a corrosive compound
generation source, (c) being cured by a curing method which rarely
causes damage to the transistor structure formed by the
semiconductor process such as RIE and allows the single-wafer
process, (d) a low dielectric constant due to high hydrophobicity
and low hygroscopicity, and (e) the capability of withstanding
formation of a copper damascene structure or the like due to
excellent mechanical strength as evidenced by a greater modulus of
elasticity.
The film forming composition of the invention includes the organic
silica sol into which the component shown by the general formula
(A1) or (A2) is introduced in which a silicon atom bonds to the
.alpha.-position or .gamma.-position of an unsaturated bond such as
a vinylalkoxysilane. An organic silica-based film having an
extremely high modulus of elasticity and lower hygroscopicity can
be obtained in a shorter time without using a large amount of
tetrafunctional silane compound component as the silane compound,
by applying and drying the film forming composition and subjecting
the dried composition to heating and ultraviolet radiation
application preferably in the absence of oxygen. When the organic
silica sol having a vinylsilane bond is applied, dried, and
irradiated with ultraviolet radiation under heating, the vinyl
group completely disappears in a short time, and the amount of
component Q (silicon atom which bonds to four oxygen atoms in the
organic silica sol) is increased to a large extent. The details of
this reaction mechanism have not been clarified. The reaction
mechanism is estimated as follows. The substituent site having the
unsaturated bond is excited by ultraviolet radiation application
and eliminated from the silicon atom, whereby the reactivity of the
silicon atom is increased. As a result, the silicon atom reacts
with the silanol present near the silicon atom so that the siloxane
site having the unsaturated bond originating in the compound 1
(trifunctional silane compound) is converted to the component Q.
This increases the crosslink density and significantly increase the
modulus of elasticity. It has been confirmed that, from the
.sup.13C-NMR measurement shown in FIG. 2, the conversion into the
component Q predominantly occurs by elimination of the carbon
unsaturated bond rather than thermal addition polymerization of the
carbon unsaturated bond.
As the technology of using the organic silica sol having a carbon
unsaturated bond represented by vinylsilane, a technology of
increasing the crosslink density by thermal polymerization of the
carbon unsaturated bond site to improve mechanical strength and
crack resistance (Japanese Patent Application Laid-Open No.
2000-327933), and a technology used to improve critical surface
tension by modifying the surface of an organic silica-based film in
order to improve adhesion to a CVD film formed as the upper layer
(Japanese Patent Application Laid-Open No. 2001-279163 and Japanese
Patent Application Laid-Open No. 2002-38091) have been known.
However, it has not been reported that the carbon unsaturated bond
site is converted into the component Q by applying ultraviolet
irradiation as in the invention, whereby the crosslink density of
the organic silica-based film is increased to obtain an organic
silica-based film having high hardness and a high modulus of
elasticity. According to the invention, since the silanol group is
consumed by dehydration polycondensation by heating and the silicon
atom activated by elimination of the carbon unsaturated group
reacts with the silanol, an organic silica-based film having high
hydrophobicity in spite of the high component Q content can be
obtained by optimizing the ratio of the residual silanol and the
carbon unsaturated bond group in the precursor. The "high component
Q content" used herein means that the content of the component Q is
preferably 40 mol % or more. In this case, the component Q includes
the component Q as the monomer and the compound 1 converted into
the component Q by the curing treatment using ultraviolet radiation
and heat.
As described above, since the silica-based film according to the
invention has a low dielectric constant and excellent mechanical
strength as evidenced by the high modulus of elasticity, the
silica-based film is particularly useful as an interlayer
dielectric for a semiconductor device such as an LSI, system LSI,
DRAM, SDRAM, RDRAM, or D-RDRAM. Moreover, the silica-based film can
be suitably used in semiconductor device applications such as an
etching stopper film, a protective film such as a surface coating
film for a semiconductor element, an intermediate layer used in the
semiconductor device manufacturing process using a multilayer
resist, an interlayer dielectric for a multilayer interconnect
substrate, a protective film and an insulating film for a liquid
crystal display element, and the like.
4. Example
The invention is described below in more detail by way of examples.
However, the invention should not be construed as being limited to
the following examples. In the examples and comparative examples,
"part" and "%" respectively indicate "part by weight" and "wt %"
unless otherwise indicated.
4.1. Examples and Comparative Examples
A film forming composition was produced and a silica-based film was
formed as described below.
4.1.1 Method of Producing Film Forming Composition
4.1.1a Example 1
A quartz flask equipped with a condenser was charged with 31.8 g of
a 20% tetrabutylammonium hydroxide aqueous solution, 143.4 g of
ultrapure water, and 448.4 g of ethanol. The mixture was stirred at
25.degree. C. After the continuous addition of 36.2 g of
vinyltrimethoxysilane as the compound 1 and 19.9 g of
methyltrimethoxysilane and 20.3 g of tetraethoxysilane as silane
compounds other than the compound 1 in one hour, the mixture was
stirred at 60.degree. C. for one hour. After cooling the reaction
solution to room temperature, 1183.6 g of propylene glycol
monopropyl ether and 30.6 g of a 20% maleic acid aqueous solution
were added. The reaction solution was concentrated under reduced
pressure until the solid content became 10% to obtain a film
forming composition 1 having a sodium content of 0.7 ppb, a
potassium content of 0.4 ppb, and an iron content of 1.7 ppb.
4.1.1b Example 2
A quartz flask equipped with a condenser was charged with 5.6 g of
a 25% tetrabutylammonium hydroxide aqueous solution, 181.0 g of
ultrapure water, and 460.9 g of ethanol. The mixture was stirred at
25.degree. C. After the continuous addition of 11.9 g of
vinyltriethoxysilane as the compound 1 and 21.2 g of
methyltrimethoxysilane and 19.5 g of tetraethoxysilane as silane
compounds other than the compound 1 in one hour, the mixture was
stirred at 60.degree. C. for one hour. After cooling the reaction
solution to room temperature, 1283.8 g of propylene glycol
monopropyl ether and 15.12 g of a 20% maleic acid aqueous solution
were added. The reaction solution was concentrated under reduced
pressure until the solid content became 10% to obtain a film
forming composition 2 having a sodium content of 0.9 ppb, a
potassium content of 0.6 ppb, and an iron content of 1.5 ppb.
4.1.1c Example 3
A quartz flask equipped with a condenser was charged with 18.0 g of
a 25% tetramethylammonium hydroxide aqueous solution, 283.6 g of
ultrapure water, and 306.3 g of ethanol. The mixture was stirred at
25.degree. C. After the continuous addition of 16.2 g of
allyltrimethoxysilane as the compound 1 and 44.6 g of
methyltriethoxysilane and 31.2 g of tetraethoxysilane as silane
compounds other than the compound 1 in one hour, the mixture was
stirred at 60.degree. C. for one hour. After cooling the reaction
solution to room temperature, 1179.8 g of propylene glycol
monopropyl ether and 48.5 g of a 20% maleic acid aqueous solution
were added. The reaction solution was concentrated under reduced
pressure until the solid content became 10% to obtain a film
forming composition 3 having a sodium content of 1.9 ppb, a
potassium content of 1.6 ppb, and an iron content of 1.0 ppb.
4.1.1d Example 4
In a quartz flask equipped with a condenser, 40.4 g of
methylvinyldimethoxysilane as the compound 1 and 103.9 g of
methyltrimethoxysilane and 95.4 g of tetraethoxysilane as silane
compounds other than the compound 1 were dissolved in 204.4 g of
propylene glycol monoethyl ether. The mixture was stirred using a
three-one motor to stabilize the solution temperature at 55.degree.
C. Then, 254.2 g of ion-exchanged water, in which 0.36 g of oxalic
acid was dissolved, was added to the solution in one hour. The
mixture was then allowed to react at 55.degree. C. for three hours.
After the addition of 917.2 g of propylene glycol monoethyl ether,
the reaction solution was cooled to room temperature. The reaction
solution was concentrated under reduced pressure until the solid
content became 10% to obtain a film forming composition 4 having a
sodium content of 0.7 ppb, a potassium content of 1.8 ppb, and an
iron content of 1.2 ppb.
4.1.1e Example 5
In a quartz flask equipped with a condenser, 42.5 g of
divinyldimethoxysilane as the compound 1 and 100.4 g of
methyltrimethoxysilane and 67.3 g of tetramethoxysilane as silane
compounds other than the compound 1 were dissolved in 181.9 g of
propylene glycol monoethyl ether. After the addition of 247.1 g of
ion-exchanged water to the solution, the mixture was stirred at
room temperature for one hour. After the addition of a solution
prepared by dissolving 0.11 g of tetrakis(acetylacetonate)titanium
in 60.6 g of propylene glycol monoethyl ether, the mixture was
allowed to react at 50.degree. C. for three hours. After the
addition of 979.2 g of propylene glycol monoethyl ether, the
reaction solution was cooled to room temperature. The reaction
solution was concentrated under reduced pressure until the solid
content became 15%. After the addition of 35.0 g of acetylacetone,
propylene glycol monoethyl ether was added so that the solid
content became 10% to obtain a film forming composition 5 having a
sodium content of 1.7 ppb, a potassium content of 0.6 ppb, and an
iron content of 1.8 ppb.
4.1.1f Example 6
A quartz flask equipped with a condenser was charged with 35.8 g of
a 20% tetrapropylammonium hydroxide aqueous solution, 225.0 g of
ultrapure water, and 349.6 g of ethanol. The mixture was stirred at
40.degree. C. After the continuous addition of 37.3 g of
vinyltrimethoxysilane as the compound 1 and 52.4 g of
tetraethoxysilane as a silane compound other than the compound 1 in
one hour, the mixture was stirred at 80.degree. C. for one hour.
After cooling the reaction solution to room temperature, 1149.2 g
of propylene glycol monopropyl ether and 34.5 g of a 20% maleic
acid aqueous solution were added. The reaction solution was
concentrated under reduced pressure until the solid content became
10% to obtain a film forming composition 6 having a sodium content
of 2.5 ppb, a potassium content of 1.6 ppb, and an iron content of
1.9 ppb.
4.1.1g Comparative Example 1
A quartz flask equipped with a condenser was charged with 39.2 g of
a 20% tetrapropylammonium hydroxide aqueous solution, 176.8 g of
ultrapure water, and 389.2 g of ethanol. The mixture was stirred at
40.degree. C. After the continuous addition of 34.5 g of
methyltrimethoxysilane and 57.3 g of tetraethoxysilane as silane
compounds other than the compound 1 in one hour, the mixture was
stirred at 80.degree. C. for one hour. After cooling the reaction
solution to room temperature, 1132.0 g of propylene glycol
monopropyl ether and 37.8 g of a 20% maleic acid aqueous solution
were added. The reaction solution was concentrated under reduced
pressure until the solid content became 10% to obtain a film
forming composition 7 having a sodium content of 1.1 ppb, a
potassium content of 1.2 ppb, and an iron content of 1.4 ppb.
4.1.1h Example 7
A quartz flask equipped with a condenser was charged with 37.6 g of
a 15% tetrabutylammonium hydroxide aqueous solution, 46.4 g of
ultrapure water, and 545.0 g of isopropanol. The mixture was
stirred at 40.degree. C. After the continuous addition of 48.6 g of
vinyltrimethoxysilane as the compound 1 and 12.7 g of
methyltrimethoxysilane and 9.7 g of tetraethoxysilane as silane
compounds other than the compound 1 in one hour, the mixture was
stirred at 80.degree. C. for one hour. After cooling the reaction
solution to room temperature, 1182.8 g of propylene glycol
monopropyl ether and 21.3 g of a 20% maleic acid aqueous solution
were added. The reaction solution was concentrated under reduced
pressure until the solid content became 10% to obtain a film
forming composition 8 having a sodium content of 2.8 ppb, a
potassium content of 1.1 ppb, and an iron content of 0.9 ppb.
4.1.2 Method of Forming silica-based Film
Organic silica-based films of Examples 8 to 17 and Comparative
Examples 2 to 7 were obtained using the composition and the curing
conditions shown in Table 1.
4.1.2a. Examples 8 to 17 and Comparative Example 5
The film forming composition obtained in (1) was applied to an
8-inch silicon wafer using a spin coating method. The coating was
dried at 90.degree. C. for one minute on a hot plate and at
200.degree. C. for one minute in a nitrogen atmosphere. The coating
was cured by applying ultraviolet radiation while heating the
coating on the hot plate to obtain an organic silica-based film
sample. Table 1 shows the type of film forming composition and the
curing conditions (type of ultraviolet radiation, heating
temperature, curing time using heating and UV application) .
As the ultraviolet radiation source, a white ultraviolet radiation
source emitting ultraviolet radiation having a wavelength of 250 nm
or less (hereinafter called "ultraviolet radiation 1") was
used.
4.1.2b Comparative Examples 2, 3, and 4
In Examples 8 to 17 and Comparative Example 5, heating and
application of the ultraviolet radiation 1 were performed at the
same time in the curing treatment. In Comparative Examples 2, 3,
and 4, samples were obtained by curing the coating by performing
only the heat treatment under the conditions shown in Table 1
without applying ultraviolet radiation.
4.1.2c Comparative Example 6
In Examples 1 to 10 and Comparative Example 4, heating and
application of the ultraviolet radiation 1 were performed at the
same time in the curing treatment. In Comparative Example 5, a
sample was obtained by curing the coating by using ultraviolet
radiation obtained by cutting off the wavelength of 250 nm or less
of the ultraviolet radiation source 1 using a UV-cut filter
(hereinafter called "ultraviolet radiation 2").
4.1.2d Comparative Example 7
In Examples 8 to 17 and Comparative Example 5, heating and
application of the ultraviolet radiation 1 were performed at the
same time in the curing treatment. In Comparative Example 7, a
sample after drying was used without performing the curing
treatment.
4.2 Evaluation Method
The organic silica-based film obtained in 4.1.(2) was evaluated as
described below.
4.2.1 Dielectric constant and .DELTA.k
A dielectric constant measurement sample was prepared by forming an
aluminum electrode pattern by a vapor deposition method on the
organic silica-based film formed on an 8-inch N-type silicon wafer
having a resistivity of 0.1 .OMEGA..cm or less using the
above-described method. The dielectric constant of the organic
silica-based film was measured by a CV method at a frequency of 100
kHz using an electrode "HP16451B" and a precision LCR meter
"HP4284A" manufactured by Agilent Technologies.
The .DELTA.k is the difference between the dielectric constant
(k@RT) measured at 24.degree. C. and 40% RH and the dielectric
constant (k@200.degree. C.) measured at 200.degree. C. in a dry
nitrogen atmosphere (.DELTA.k=k@RT-k@200.degree. C). An increase in
the dielectric constant of the film due to moisture absorption can
be evaluated by the .DELTA.k. An organic silica-based film is
determined to have high hygroscopicity when the .DELTA.k is 0.15 or
more.
4.2.2 Modulus of Elasticity of Silica-based Film
A Berkovich type indenter was installed in a nanohardness tester
(Nanoindenter XP) manufactured by MTS, and the modulus of
elasticity of the insulating film formed by the above-described
method was measured by a continuous stiffness measurement
method.
4.2.3 FT-IR
The FT-IR measurement was carried out using an FT-IR spectrometer
(FTS 3000) manufactured by Digilab Japan Co., Ltd.
4.2.4 .sup.13C-CPMAS NMR
The sample was packed into a zirconia rotor having an outer
diameter of 7 mm, and .sup.13C-NMR measurement was carried out by a
cross-polarization magic angle spinning (CP-MAS) method using a 300
MHz Fourier transform NMR spectrometer (Advance 300 manufactured by
Bruker). The measurement was carried out at a measurement
temperature of 30.degree. C., a pulse interval of 5 sec, a sample
tube rotational speed of 3000 to 7000 Hz, a center frequency of
75.48 MHz, a frequency range of 26.46 kHz, a data point of 16 k,
and a number of transients of 10 to 5,000. Glycine was subjected to
the measurement in advance as a chemical shift standard sample. The
decoupler frequency offset value when correcting the peak of a
carbonyl group to 176.03 ppm was read, and the value of each sample
was corrected by inputting the value in the measurement of each
sample.
TABLE-US-00001 TABLE 1 Heating temperature Modulus of Example
Composition Ultraviolet radiation (.degree. C.) Curing time (min)
Dielectric constant .DELTA.k elasticity Example 8 2 1 400 1 2.20
0.06 4.2 Example 9 2 1 400 3 2.22 0.05 5.0 Example 10 2 1 400 6
2.25 0.06 6.4 Example 11 1 1 400 3 2.32 0.06 8.4 Example 12 8 1 400
3 2.62 0.12 13.3 Example 13 6 1 400 3 2.35 0.08 8.8 Example 14 3 1
400 3 2.25 0.05 4.8 Example 15 4 1 400 3 2.91 0.09 9.5 Example 16 5
1 400 3 2.82 0.08 10.0 Example 17 2 1 100 6 2.25 0.08 4.5
Comparative Example 2 2 None 400 6 (only heating) 2.36 0.21 3.20
Comparative Example 3 7 None 420 60 (only heating) 2.24 0.10 5.2
Comparative Example 4 7 None 420 6 (only heating) 2.30 0.20 3.1
Comparative Example 5 7 1 400 3 2.24 0.16 4.3 Comparative Example 6
2 2 400 6 2.20 0.15 3.0 Comparative Example 7 2 None None -- -- --
--
4.3 Evaluation Results 4.3.1 Dielectric Constant, .DELTA.k, and
Modulus of Elasticity
The dielectric constant, .DELTA.k, and modulus of elasticity were
determined for the silica-based films obtained in Examples 8 to 17
and Comparative Examples 2 to 7. The evaluation results are shown
in Table 1.
In Examples 8 to 10, the composition 2, in which the content of the
compound (compound 1) shown by the general formula (A) effective
for curing by ultraviolet radiation (UV curing) was 20 mol %, was
cured (UV cured) by applying ultraviolet radiation for 1, 3, or 6
minutes. In Comparative Example 2, the composition 2 was cured by
heating for six minutes.
In Examples 8 to 10, a low .DELTA.k and a high modulus of
elasticity were obtained, whereby an insulating film having
excellent characteristics was obtained. In Comparative Example 2,
since the composition was cured by heating at the same temperature
without applying ultraviolet radiation, an insulating film having a
considerably high .DELTA.k was obtained. This is considered to be
because the reaction of the silane compound did not sufficiently
proceed so that the amount of residual silanol group was not
sufficiently decreased. From these results, it was found that the
curing treatment by heating and ultraviolet radiation application
is indispensable for the composition of the invention. It was also
found that the composition of the invention exhibits excellent
characteristics in a sufficiently short curing time which enables
single-wafer processing when the composition is cured by heating
and ultraviolet radiation application.
In Comparative Examples 3 and 4, the composition 7 in which the
content of the compound 1 was 0 mol % was used. In Comparative
Example 3, a dielectric constant, .DELTA.k, and modulus of
elasticity effective as a low-dielectric-constant interlayer
dielectric were obtained as a result of curing the composition by
heating for a long time of 60 minutes. In Comparative example 4 in
which the composition was cured at a lower temperature and a
shorter time in comparison with Comparative Example 3, a high
.DELTA.k and a low modulus of elasticity were obtained. This
suggests that the condensation reaction of the silane compound did
not proceed in Comparative Example 4 and that the reaction does not
proceed by curing by heating for a short time.
In Comparative Example 5 and Examples 9, 11, and 12, the
composition in which the content of the compound 1 was respectively
0 mol %, 20 mol %, 50 mol %, and 70 mol % was cured by applying
ultraviolet radiation for three minutes.
In Comparative Example 5, a high .DELTA.k and a low modulus of
elasticity were obtained, whereby an insulating film having
unfavorable characteristics was obtained. In Examples 9 and 11, a
low .DELTA.k and a high modulus of elasticity were obtained,
whereby an insulating film having excellent characteristics was
obtained. In Example 12, since a very high modulus of elasticity
was obtained, it was confirmed that curing proceeded to a greater
degree in comparison with Examples 9 and 11. However, the
dielectric constant was increased and the .DELTA.k was increased to
some extent.
It is considered that, from the FT-IR and NMR results as described
later, the reaction caused by UV curing proceeds by elimination of
the substituent of the compound 1. In the case where the
concentration of the substituent is too high, the side reaction
between the substituents occurs, whereby the dielectric constant
and the .DELTA.k are increased. From these results, it was found
that the content of the compound 1 is preferably 70 mol % or
less.
In Example 13, the composition of the composition of Example 11
other than the compound 1 was changed. In Example 13, a low
.DELTA.k and a high modulus of elasticity were obtained in the same
manner as in Example 11.
In Examples 14 to 16, the substituent of the compound 1 included in
the composition 2 was changed from the vinyl group to the allyl
group, methyl group+vinyl group, and vinyl group+vinyl group,
respectively. In Examples 14 to 16, an insulating film having a
high modulus of elasticity and a low .DELTA.k while exhibiting a
sufficiently low dielectric constant was obtained.
Example 17 is the same as Example 10 except that the UV curing
temperature was set at 100.degree. C. In Example 17, an insulating
film having excellent characteristics with a low .DELTA.k and a
high modulus of elasticity comparable to those of Example 8, in
which the curing time of Example 10 was changed from six minutes to
one minute, was obtained. However, the modulus of elasticity was
lower than that of Example 8. This suggests that the condensation
reaction of the silane compound proceed to a greater extent at a
higher temperature.
Comparative Example 6 is the same as Example 10 except for using
the ultraviolet radiation 2 obtained by cutting off the wavelength
of 250 nm or less instead of the ultraviolet radiation 1 of Example
10. In Comparative Example 6, since a high .DELTA.k and a low
modulus of elasticity were obtained, it was found that the
condensation reaction of the silane compound did not sufficiently
proceed. Therefore, it was found that the wavelength effective for
UV curing is 250 nm or less.
4.3.2 FT-IR
The infrared absorption spectrum was determined for the
silica-based films obtained in Examples 8 to 10 and Comparative
Examples 2 and 7.
The coatings of Examples 8 to 10 were obtained by curing the
composition 2 by applying ultraviolet radiation for 1, 3, and 6
minutes, respectively, under heating. The coating of Comparative
Example 2 was obtained by curing the composition by heating, and
the coating of Comparative Example 7 was not provided with the
curing treatment. FIG. 1 shows the FT-IR results of these coatings.
In FIG. 1, a line indicated by a symbol "a" indicates the results
of Comparative Example 7, a line indicated by a symbol "b"
indicates the results of Comparative Example 2, and lines indicated
by symbols "c", "d", and "e" respectively indicate the results of
Examples 8, 9, and 10.
As shown in FIG. 1, peaks of C.dbd.C and .dbd.CH.sub.2 were
observed in the spectra of Comparative Examples 2 and 7. On the
other hand, it was confirmed that these peaks were decreased or
disappeared in Examples 8 to 10. It was found that these peaks are
decreased as the ultraviolet radiation application time is
increased.
4.3.3 .sup.13C-CPMAS NMR
The amount of the substituent of the composition in the film was
evaluated for the silica-based films obtained in Example 10 and
Comparative Example 2 by NMR.
FIG. 2 shows the .sup.13C-CPMAS NMR results obtained for Example 10
in which the composition 2 including a vinyl group was cured by
heating and UV curing and Comparative Example 2 in which the
composition was cured only by heating. In FIG. 2, a line indicated
by a symbol "a" indicates the results of Example 10, and a line
indicated by a symbol "b" indicates the results of Comparative
Example 2.
As shown in FIG. 2, it was confirmed that, while the peak of an
Si-vinyl group was observed in the spectrum of Comparative Example
2, this peak disappeared in Example 10.
From the FT-IR and NMR results, it was found that the vinyl group
of the compound 1 was eliminated by heating and UV curing. It is
considered that elimination of the vinyl group causes the
elimination site to react with the silanol group, whereby the
condensation proceeds. Since the vinyl group is eliminated only by
ultraviolet radiation application, it is considered that excitation
by ultraviolet radiation is necessary for elimination of the vinyl
group.
As is clear from the above results, it was confirmed that the
invention enables formation of a silica-based film having
significantly improved characteristics (particularly modulus of
elasticity and .DELTA.k) in comparison with the comparative
examples. Therefore, the silica-based film obtained according to
the invention exhibits excellent mechanical strength and a low
dielectric constant, and can be suitably used as an interlayer
dielectric for a semiconductor device and the like.
Although only some embodiments of the present invention have been
described in detail above, those skilled in the art will readily
appreciate that many modifications are possible in the embodiments
without materially departing from the novel teachings and
advantages of this invention. Accordingly, all such modifications
are intended to be included within scope of this invention.
* * * * *
References